Glossary
Sleep Cycle
A sleep cycle is a complete sequence of sleep stages (light sleep, deep sleep, and REM) that repeats approximately every 90 minutes throughout the nig...
REM Sleep
REM (Rapid Eye Movement) sleep is a sleep stage characterized by rapid eye movements, vivid dreaming, and temporary muscle paralysis. It's crucial for...
Deep Sleep (Slow-Wave Sleep)
Deep sleep, also called slow-wave sleep (SWS) or Stage 3 sleep, is the most restorative sleep phase. During deep sleep, your body releases growth horm...
Sleep Latency
Sleep latency is the time it takes from getting into bed to falling asleep. The average for healthy adults is 10–20 minutes. Latency under 5 minutes m...
Circadian Rhythm
Your circadian rhythm is a roughly 24-hour internal clock that regulates sleep-wake cycles, hormone release, body temperature, and digestion. It's pri...
Melatonin
Melatonin is a hormone produced by the pineal gland that signals your body to prepare for sleep. Production increases in response to darkness and is s...
Sleep Debt
Sleep debt is the cumulative difference between the amount of sleep you need and the amount you actually get. If you need 8 hours but sleep 6, you acc...
Sleep Inertia
Sleep inertia is the groggy, disoriented feeling you experience immediately after waking up. It's most severe when you wake from deep sleep (Stage 3) ...
Chronotype
Your chronotype is your genetically influenced preference for sleeping and waking times. Common classifications include morning types (larks), evening...
Adenosine
Adenosine is a neurotransmitter that accumulates in your brain during waking hours, creating increasing pressure to sleep (called sleep pressure or ho...