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)
• Selected books and review papers (e.g., Walker, "Why We Sleep").

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].