Terms of Use

General guidance, not medical advice

The tools and articles on this site are for general guidance only. They are not a substitute for professional medical, psychological, or clinical advice. If you have persistent sleep issues or other health concerns, please consult a qualified clinician.

No warranty

This service is provided as-is. While we try to base recommendations on commonly accepted sources, we do not guarantee the completeness, accuracy, or suitability of any output for a specific purpose.

Restricted use

Do not use the service in ways that place excessive load on the infrastructure, violate applicable laws, or infringe the rights of others.

References (Sources)

"References" on this site refers to the primary sources behind our recommendations — for example, around sleep duration or the 90-minute sleep cycle. We prioritize public institutions and well-established medical bodies, then peer-reviewed reviews, and only individual studies when necessary.

Main sources we rely on

• CDC / NIH — adult recommended sleep duration (7+ hours for adults, age-based ranges), and the CDC Yellow Book on jet lag disorder.
• AASM (American Academy of Sleep Medicine) / SRS — age-based sleep duration guidelines and joint consensus statement on recommended sleep.
• National Sleep Foundation (NSF) — recommended sleep range for adults (7–9 hours, ages 18–64).
• Japan's Ministry of Health, Labour and Welfare — Sleep Guide for Health Promotion.
• MSD Manual Consumer Version (Japanese edition) — circadian rhythm sleep disorders, including the jet lag type.
• Sleep Foundation — sleep cycles, how much deep sleep you need, sleep hygiene, light and sleep, morning light, jet lag, social jet lag, sleep debt, napping, caffeine guidance, showering before bed, stretching before bed, how to fall asleep fast, alcohol and sleep, "Is 6 Hours of Sleep Enough?", how to become a morning person, sleep schedules for night shift workers, sleep inertia, and sleeping positions.
• Cleveland Clinic — sleep hygiene, 4-7-8 breathing, fatigue after full-night sleep, Familial Natural Short Sleep, power naps, the military sleep method, the best bedroom temperature for sleep, pink noise for sleep, and how to become a morning person.
• Baniassadi A, et al., Science of The Total Environment (2023) — home monitoring study of nighttime bedroom temperature and sleep in adults aged 65 and over (about 11,000 nights from 50 adults; sleep was most efficient at 68-77°F / 20-25°C).
• Andrew Weil, M.D. (drweil.com) — original instructions for the 4-7-8 breathing exercise.
• Lloyd "Bud" Winter, "Relax and Win: Championship Performance" (1981) — the book the military sleep method is usually traced to.
• The Conversation — expert commentary on the military sleep method and normal sleep onset.
• World Health Organization (WHO) — Housing and health guidelines (recommended minimum indoor temperature).
• Mayo Clinic — general sleep tips, napping do's and don'ts, sleep apnea information, and how much sleep is enough for health.
• Hospital for Special Surgery (HSS) — physical therapist guidance on stretches to do before bed.
• NASA (Rosekind MR et al., NASA Technical Memorandum 108839, 1994) — planned cockpit rest study on short in-flight naps, alertness, and performance in long-haul crews.
• CDC / NIOSH — napping as a fatigue countermeasure (nap duration and timing for shift workers), and NIOSH training for nurses on shift work and long work hours.
• Harvard Health Publishing — resetting the circadian clock for jet lag, paying back sleep debt, and how much sleep you actually need.
• NHS (UK) — insomnia self-help guidance and tips for falling asleep.
• NPR — reporting on wind-down routines and bedtime rituals.
• U.S. Food and Drug Administration (FDA) — caffeine intake guidance.
• European Food Safety Authority (EFSA) — caffeine safety assessment.
• American College of Obstetricians and Gynecologists (ACOG) — caffeine during pregnancy and breastfeeding.
• StatPearls (NIH National Library of Medicine) — caffeine withdrawal symptoms and timeline.
• Juliano LM, Griffiths RR, Psychopharmacology (Berl) 2004 — critical review of caffeine withdrawal, covering the type, incidence, severity, and time course of symptoms.
• Reichert CF et al., Frontiers in Nutrition 2022 — review of caffeine pharmacokinetics and how long it takes to recover after stopping caffeine intake.
• USDA FoodData Central / Japan's Standard Tables of Food Composition — caffeine values for common foods and drinks.
• Drake C et al., Journal of Clinical Sleep Medicine 2013 — caffeine effects on sleep at 0, 3, and 6 hours before bedtime.
• Lara B et al., PLoS One 2019 — time course of tolerance to the performance benefits of caffeine (11 healthy active adults, 3 mg/kg daily for 20 days, double-blind crossover).
• Weibel J et al., Journal of Biological Rhythms 2021 — regular caffeine intake, REM sleep promotion and sleep quality in healthy men (20 participants, 150 mg three times daily for 10 days, double-blind randomized crossover).
• Vallat R, Walker MP et al., Nature Communications 2022 — how prior-night sleep, physical activity, and food intake relate to waking alertness.
• Wittmann M, Roenneberg T et al., Chronobiology International 2006 — social jetlag and the misalignment of biological and social time.
• Roenneberg T et al., Current Biology 2012 — social jetlag and its association with body weight.
• Haghayegh S et al., Sleep Medicine Reviews 2019 — systematic review and meta-analysis on warm baths or showers before bedtime and sleep onset.
• Wang F et al., Sleep Medicine Reviews 2016 — systematic review of meditative movement (tai chi, qigong, yoga) and sleep quality.
• Scullin MK et al., Journal of Experimental Psychology: General 2018 — polysomnographic study comparing bedtime to-do lists and completed activity lists on sleep onset.
• Baikie KA, Wilhelm K, Advances in Psychiatric Treatment 2005 — review of emotional and physical health benefits of expressive writing.
• Vierra J et al., Physiological Reports 2022 — effects of 4-7-8 breathing on heart rate variability and blood pressure in sleep-deprived healthy young adults.
• Craig Ballantyne (Early to Rise) — the coach the 10-3-2-1-0 sleep rule is usually traced to.
• ColumbiaDoctors (Columbia University Irving Medical Center) — explainer on the 10-3-2-1-0 sleep routine.
• Sundelin T et al., Journal of Sleep Research 2023 — study on intermittent morning alarms (snoozing) and their effects on sleep, cognition, cortisol, and mood.
• Mattingly SM et al., SLEEP 2022 — field study of snoozing as a common method of waking, sleep in the final hour before waking, and resting heart rate.
• Nikbakhtian S et al., European Heart Journal — Digital Health 2021 — UK Biobank cohort study on accelerometer-derived sleep onset timing and cardiovascular disease incidence.
• Luc P. Beaudoin (Simon Fraser University / mySleepButton) — the do-it-yourself instructions and theory behind the cognitive shuffle (serial diverse imagining), with conference abstracts at SLEEP 2016 and World Sleep 2019.
• Time — reporting and expert commentary on cognitive shuffling.
• Belenky G, Wesensten NJ, Thorne DR, et al., Journal of Sleep Research 2003 — sleep dose-response study on performance degradation and recovery under sleep restriction.
• Lo JC, Ong JL, Leong RL, Gooley JJ, Chee MWL, Sleep 2016 — cognitive performance, sleepiness, and mood in partially sleep-deprived adolescents (the Need for Sleep study).
• Hilditch CJ, McHill AW, Nature and Science of Sleep 2019 — review of sleep inertia after short naps and following sleep loss.
• Ochab JK et al., PLOS ONE 2021 — observed changes in human functioning during induced sleep deficiency and recovery periods after a single all-nighter.
• National Center for Complementary and Integrative Health (NCCIH / NIH) — meditation and mindfulness: effectiveness and safety.
• Black DS et al., JAMA Internal Medicine 2015 — randomized clinical trial of mindfulness meditation and sleep quality in older adults with sleep disturbances.
• Rusch HL et al., Annals of the New York Academy of Sciences 2019 — systematic review and meta-analysis of mindfulness meditation and sleep quality.
• Jon Kabat-Zinn, "Full Catastrophe Living" (1990, revised 2013) — the original book behind MBSR and the body scan meditation.
• UCLA Mindful Awareness Research Center (MARC) — free guided meditations, including body scans.
• Zhou J et al., Journal of Theoretical Biology 2012 — study of steady pink noise and sleep stability.
• Capezuti E et al., Journal of Clinical Sleep Medicine 2022 — systematic review of auditory stimulation (white noise, pink noise, and combinations) and sleep.
• Papalambros NA et al., Frontiers in Human Neuroscience 2017 — acoustic stimulation synchronized to slow oscillations and memory in older adults.
• Riedy SM et al., Sleep Medicine Reviews 2021 — systematic review of continuous noise as a sleep aid.
• Basner M et al., Sleep 2026 — laboratory trial of pink noise and aircraft noise on sleep stages (with the Penn Medicine news release).
• Hugh SC et al., Pediatrics 2014 — study of maximum output levels of infant sound machines.
• Japan's MHLW e-Health Net — guidance on sleep for shift workers.
• Minors DS, Waterhouse JM, International Journal of Chronobiology 1981 — the original study of anchor sleep as a synchronizer of daily rhythms on irregular routines.
• Garde AH et al., Scandinavian Journal of Work, Environment & Health 2020 — recommendations for scheduling night shift work to reduce health and safety risks.
• Facer-Childs ER et al., Sleep Medicine 2019 — a small non-pharmacological intervention study in which night owls shifted their sleep timing about two hours earlier over three weeks.
• Jones SE et al., Nature Communications 2019 — genome-wide association analyses of chronotype in 697,828 individuals, on the genetics of being a morning or evening person.
• Swami Satyananda Saraswati, "Yoga Nidra" (Bihar School of Yoga) — the book behind the form of yoga nidra in wide use today
• Singh S et al., Sleep and Breathing 2026 — systematic review and meta-analysis of yoga nidra for sleep disturbances and insomnia (certainty of evidence rated very low)
• Dutta A, Mooventhan A et al., Journal of Integrative and Complementary Medicine 2026 — systematic review of yoga nidra for sleep disorders
• Datta K et al., PLOS ONE 2023 — sleep and cognitive task performance in novices practising yoga nidra
• Fialoke S et al., Scientific Reports 2024 — changes in brain functional connectivity during yoga nidra practice
• Kitamura S et al., Scientific Reports 2016 — estimating individual optimal sleep duration and potential sleep debt (15 healthy young men, nine-day extended-sleep protocol; the source of the "about four days per lost hour" figure)
• Japan's Ministry of Health, Labour and Welfare, e-Healthnet — "Good sleep and lifestyle habits", on morning light advancing the body clock and evening light delaying it.
• NIH NIGMS — fact sheet on circadian rhythms, on light and dark as the strongest influences on the body clock.
• Thompson A, Jones H, Gregson W, Atkinson G, European Journal of Applied Physiology 2014 — crossover trial of dawn simulation during the last 30 minutes of sleep on sleep inertia and post-waking performance (8 participants).
• Golden RN et al., American Journal of Psychiatry 2005 — review and meta-analysis of light therapy for mood disorders, including dawn simulation in seasonal affective disorder (five studies, effect size 0.73, 95% CI 0.37 to 1.08).
• NIH / NHLBI — "How Sleep Works: Sleep Phases and Stages", on the NREM and REM stages and how they repeat through the night.
• NCBI StatPearls — "Physiology, Sleep Stages", on the physiology of each stage and the typical share of the night each one takes.
• NIH / PMC — "Sleep in Normal Aging", on how sleep architecture shifts with age.
• CDC / NIOSH — Module 3, on impairment from sleep deprivation being comparable to impairment from alcohol.
• Sleep Foundation — "How Is Sleep Different for Men and Women?", on reported differences in sleep duration and stage balance between men and women.
• NIH / PMC — sleep cycle duration in healthy term infants (about 47 to 50 minutes).
• Sleep Foundation — "Baby Sleep Cycles", on how an infant cycle stretches toward the adult 90 minutes by around age five.
• Japan's Ministry of Health, Labour and Welfare, medical fee schedule — the official point values for first visits, follow-up visits, tests, and online consultations that our Japanese cost articles convert at 10 yen per point.
• Shirobon — an item-by-item reference to the Japanese fee schedule, used to locate the category a given test or visit falls under.
• Japan's MHLW, overview of the Guidelines for the Proper Implementation of Online Medical Care — the drugs not prescribed at an online first visit (narcotics and psychotropics, high-risk drugs, and prescriptions of 8 days or more).
• Japan's National Tax Agency — No.1120 (how the medical expense deduction is calculated, including the 100,000 yen threshold and the 2 million yen cap), No.1122 (which medical expenses qualify), and No.1128 (worked examples for dental costs).
• AASM — Kapur VK, Auckley DH, Chowdhuri S, et al., Clinical Practice Guideline for Diagnostic Testing for Adult Obstructive Sleep Apnea (Journal of Clinical Sleep Medicine, 2017). The basis for our statement that a negative or inconclusive home sleep apnea test is usually followed by an in-lab study rather than a repeat home test.
• Belenky G, Wesensten NJ, Thorne DR, et al., Journal of Sleep Research 2003;12(1):1-12 — a sleep dose-response study on how performance degrades under sleep restriction and how it comes back during recovery.
• Lo JC, Ong JL, Leong RL, Gooley JJ, Chee MWL, Sleep 2016;39(3):687-698 — cognitive performance, sleepiness, and mood in partially sleep deprived adolescents.
• Ochab JK, et al., PLOS ONE 2021;16(9):e0255771 — changes in human functioning during induced sleep deficiency and the recovery period that follows.
• Sleep Foundation — How to Pull an All-Nighter: tips, risks, and next-day recovery.
• Sleep Foundation — What All-Nighters Do To Your Cognition.
• Sleep Foundation — Best Temperature for Sleep, used for the bedroom temperature range in our wind-down and bedroom articles.
• Cleveland Clinic — Sleep Deprivation: What It Is, Symptoms, Treatment & Stages.
• American Academy of Sleep Medicine (AASM), Healthy Sleep Habits — no fixed numeric bedroom temperature target; the emphasis is on a comfortable, cool, dark room.
• Spiegel K, et al., Annals of Internal Medicine 2004 — sleep curtailment in healthy young men, with changes in leptin, ghrelin, hunger, and appetite.
• Fujiwara Y, et al., American Journal of Gastroenterology 2005 — a case-control study of dinner-to-bed time and gastro-esophageal reflux disease.
• Allison KC, et al., International Journal of Eating Disorders 2010 — the proposed diagnostic criteria for night eating syndrome.
• Kinsey AW, Ormsbee MJ, Nutrients 2015 — a review of the health impact of nighttime eating that separates small nutrient-dense intakes from large mixed meals.
• St-Onge MP, et al., Advances in Nutrition 2016 — a review of the effects of diet on sleep quality, covering milk, fatty fish, tart cherry juice, and kiwifruit, with the findings described as preliminary.
• American Diabetes Association, Hypoglycemia (Low Blood Glucose) — the symptoms and the 15 grams of fast-acting carbohydrate, recheck after 15 minutes approach.
• NHS (UK), Low blood sugar (hypoglycaemia) — the symptoms and what to do.
• USDA FoodData Central — used for the approximate energy values in our food and sleep articles.
• Japan's Ministry of Education, Culture, Sports, Science and Technology, food composition database — used for the approximate energy values in the Japanese food and sleep articles.
• Black DS, O'Reilly GA, Olmstead R, Breen EC, Irwin MR, JAMA Internal Medicine 2015;175(4):494 — a randomized clinical trial of mindfulness meditation and sleep quality in older adults with sleep disturbances.
• Rusch HL, Rosario M, Levison LM, et al., Annals of the New York Academy of Sciences 2019;1445(1):5-16 — a systematic review and meta-analysis of randomized controlled trials on mindfulness meditation and sleep quality.
• Beaudoin LP, Digdon N, O'Neill K, et al. (2016) — a conference abstract from SLEEP 2016 testing the cognitive shuffle with university students.
• Beaudoin L, Lemyre A, Pudlo M, Bastien C, Sleep Medicine 2019;64(Suppl 1):S29 — an abstract from World Sleep 2019.
• Japan's Ministry of Health, Labour and Welfare, Health Japan 21 Action Support System — the entry on shift work sleep disorder.
• Philips Wake-Up Light HF3520 user manual — light output and sunrise simulation time.
• Philips Wake-Up Light HF3650 user manual — the same figures for the later model.
• Totonoe Light user guide (the specification table for the TTNL-01), used for the illuminance figures in our wake-up light article.
• moonmoon's official column on the inti4 (illuminance and the measuring distance).
• Sony ICF-C1T operating instructions — how the backup battery keeps the clock and alarm working during a power interruption.
• Japan's National Consumer Affairs Center, "Curtains whose blackout labels differed from the grading widely used in Japan" (2024) — on mismatches between listed blackout grades and measured values.
• Gifu Prefectural Industrial Technology Center newsletter, October 2014 — the NIF blackout grades and the JIS L 1055 method A test.
• Obayashi K, Saeki K, Kurumatani N. Bedroom light exposure at night and the incidence of depressive symptoms: the HEIJO-KYO cohort. Am J Epidemiol 2018.
• Hu RF et al. Effects of earplugs and eye masks on nocturnal sleep, melatonin and cortisol in a simulated ICU environment. Crit Care 2010.
• RCA RCD20 user manual — battery back-up operation and how long a fresh battery holds the settings.
• Seiko Clock radio-controlled table clock manual FDL-003J (in Japanese) — backup battery, display brightness and alarm specifications.
• Sonic Alert SBB500SS-v3 operation instructions — two alarms, wake-up mode, alarm duration, dimmer and battery backup, used in our alarm clock article.
• CMS (Centers for Medicare & Medicaid Services) — Medicare approved amounts by geography and service for sleep tests, office visits, and durable medical equipment.
• Medicare.gov — what Medicare covers for sleep studies, CPAP devices, and telehealth, and the share left to the patient.
• CMS fact sheet — the Medicare Part B premium and annual deductible for the current year.
• FDA 510(k) database — premarket clearance records for the home sleep apnea test devices we name.
• AASM — the clinical practice guideline on behavioural and psychological treatments for insomnia.
• Published price lists from clinics, manufacturers, and retailers — cash prices for sleep centres, online consultations, CPAP machines, and replacement parts. Each cost article lists the ones it uses with the date we checked them.
• Selected books and review papers (e.g., Walker, "Why We Sleep").
• Headspace — "How to Build a Perfect Wind-Down Routine", on the steps of an evening wind-down.
• Medical News Today — "What is the 4-7-8 breathing technique?", a plain-language explainer of the method.
• Frontiers in Psychiatry 2025 — screen use after bedtime and insomnia symptoms.
• The University of Texas at Austin — press release on the warm bath 1-2 hours before bedtime study.
• Hal Elrod, "The Miracle Morning" — the origin of the SAVERS routine.
• Robin Sharma, "The 5 AM Club" — the 20/20/20 formula.
• 988 Suicide & Crisis Lifeline (US) — the call, text, and chat crisis line.
• International Association for Suicide Prevention — crisis centre directory covering more than 150 countries.

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Updates

When we add new sources or change the evidence base behind a tool, we will update this page. See the rule documented in the project's CLAUDE.md.

Contact

Questions about these terms can be sent to [email protected].