front 1 Circadian rhythm | back 1 The state of being alert (beta waves) or relaxed (alpha waves) before falling asleep. |
front 2 Dreams | back 2 The lightest phase of sleep where a person is easily awoken. Brain activity shifts to theta waves |
front 3 Electroencephalograph (EEG) | back 3 A period of light sleep where heart rate and temperature drop. The EEG shows distinct "sleep spindles" and "K-complexes". |
front 4 Hypersomnia | back 4 Excessive daytime sleepiness despite getting enough nighttime sleep. |
front 5 Insomnia | back 5 Persistent difficulty falling or staying asleep. |
front 6 Melatonin | back 6 A hormone produced in response to darkness that helps signal the body it is time to sleep. |
front 7 Napping | back 7 Short periods of sleep during the day, which may or may not relieve sleepiness depending on the underlying condition. |
front 8 Narcolepsy | back 8 A neurological disorder causing sudden "sleep attacks" and a disordered regulation of REM sleep. |
front 9 Night Terrors | back 9 Night terrors occur in NREM sleep and involve intense fear without a clear dream, while nightmares are scary dreams occurring in REM sleep. |
front 10 Nightmares | back 10 Night terrors occur in NREM sleep and involve intense fear without a clear dream, while nightmares are scary dreams occurring in REM sleep. |
front 11 Parasomnia | back 11 disruptive sleep disorders involving undesirable physical behaviors or experiences—such as sleepwalking, sleep terrors, or nightmares—occurring during sleep, upon waking, or between sleep stages. |
front 12 Restless Legs Syndrome | back 12 a common neurological disorder characterized by an irresistible urge to move the legs, typically triggered by uncomfortable sensations like crawling or tingling when resting or at night. |
front 13 Sleep | back 13 a vital, active process necessary for cognitive function, memory consolidation, and physical restoration. |
front 14 Sleep apnea | back 14 a common, serious disorder where breathing repeatedly stops and starts during sleep, preventing restful sleep and lowering blood oxygen levels. |
front 15 Sleep deprivation | back 15 : The condition of not getting enough sleep, leading to cognitive impairment and health risks. |
front 16 Sleep paralysis | back 16 The brain "paralyzes" voluntary muscles (muscle atonia) to prevent acting out dreams. |
front 17 Sleep study | back 17 (polysomnography) is the primary clinical tool used to diagnose these conditions by recording brain waves, oxygen levels, and movements overnight. |
front 18 Snoring | back 18 the sound caused by air forcing its way through blocked or narrowed airways, making throat tissues vibrate during sleep |
front 19 Stage 1 (Non-REM) sleep | back 19 the brief, lightest transitional phase between wakefulness and sleep, typically lasting 1–7 minutes and making up 2-5% of total sleep. |
front 20 Stage 2 (Non-REM) sleep | back 20 a period of light sleep, often lasting 10–25 minutes, that constitutes about 50% of total adult sleep time. |
front 21 Stage 3 (Non-REM) sleep | back 21 Also known as slow-wave sleep or deep sleep, characterized by slow delta waves. This stage is critical for tissue repair and growth. |
front 22 Stage 4 (REM Sleep) | back 22 high brain activity, vivid dreaming, rapid eye movements, and temporary muscle paralysis. |
front 23 Somnambulism | back 23 a disorder where complex behaviors (like walking) occur during deep non-REM (N3) sleep, typically in the first third of the night |
front 24 Wakefulness | back 24 a state of active alertness and consciousness, distinct from sleep, driven by complex neural networks involving neurotransmitters like norepinephrine, serotonin, and orexin. |