Most adults need 6-8 hours of sleep per night to function optimally.

Wakefulness is not a stage of sleep, but rather the state of being awake.

REM sleep is primarily responsible for memory consolidation, the process by which memories are stored in the brain.

Melatonin is the hormone that regulates the sleep-wake cycle, promoting sleepiness at night and wakefulness during the day.

Microsleep is the term for the brief period of wakefulness that occurs between sleep cycles, typically lasting for a few seconds.

All of the above are common symptoms of sleep deprivation.

Insomnia is the term for the inability to fall asleep or stay asleep.

All of the above are common causes of insomnia.

Sleep apnea is the condition in which a person repeatedly stops breathing during sleep.

All of the above are common symptoms of sleep apnea.

Restless legs syndrome is the condition in which a person has an irresistible urge to move their legs while sleeping.

All of the above are common symptoms of restless legs syndrome.

Narcolepsy is the condition in which a person suddenly falls asleep during the day.

All of the above are common symptoms of narcolepsy.

Hypnagogic hallucination is the term for the condition in which a person experiences vivid, dream-like hallucinations while falling asleep.