Circadian rhythm

the physical, mental, and behavioral changes an organism experiences over a 24-hour cycle.

Dreams

stories and images that our minds create while we sleep.

Electroencephalograph (EEG)

a test that measures electrical activity in the brain using small, metal discs.

Hypersomnia

a condition in which you feel extreme daytime sleepiness despite getting sleep that should be adequate (or more than adequate).

Insomnia

a common sleep disorder.

Melatonin

a hormone that your brain produces in response to darkness.

Napping

a midday nap can enhance alertness, mood, memory, and reduce stress.

Narcolepsy

a chronic neurological disorder that affects the brain's ability to control sleep-wake cycles.

Night Terrors

a sleep disorder in which a person quickly awakens from sleep in a terrified state.

Nightmares

bad dreams that wake you up.

Parasomnia

occur in a state that lies between sleep and wakefulness.

Restless Legs Syndrome

a condition that causes a very strong urge to move the legs.

Sleep

a period during which the brain is engaged in a number of activities necessary to life

Sleep apnea

a potentially serious sleep disorder in which breathing repeatedly stops and starts.

Sleep deprivation

when you aren't getting enough sleep, or your sleep is of poor quality.

Sleep paralysis

a feeling of being conscious but unable to move.

Sleep study

a test used to diagnose sleep disorders.

Snoring

the hoarse or harsh sound that occurs when air flows past relaxed tissues in your throat, causing the tissues to vibrate as you breathe.

Stage 1 (Non-REM) sleep

when heartbeat, eye movements, brain waves, and breathing activity begin to taper down.

Stage 2 (Non-REM) sleep

still light sleep, but deeper than stage 1.

Stage 3 (Non-REM) sleep

deep sleep.

Stage 4 (REM Sleep)

an even deeper sleep where the brain waves further slow and sleepers are very difficult to wake.

Somnambulism

sleepwalking

Wakefulness

a daily recurring brain state and state of consciousness in which an individual is conscious and engages in coherent cognitive and behavioral responses to the external world.