The sleep stage that is a transition from wakefulness to sleep.

When it comes to dreams, wish fulfillment theory is accredited to this psychologist.

A sleep disorder characterized by high arousal and an appearance of being terrified.

Psychedelic drugs that distort perceptions and evoke sensory images in the absence of sensory input.

State of consciousness that occurs seemingly without effort, typically when we want to momentarily escape reality.

A recurring sleep stage during which vivid dreams commonly occur.

The tendency for REM sleep to increase following sleep deprivation.

One of the most common sleep disorders; recurring problems in falling or staying asleep.

Amphetamines, caffeine, cocaine, and nicotine are all examples of this category of drug.

The state of consciousness that encompasses the thoughts, feelings, and perceptions that occur when we are reasonably alert.

The large, slow brain waves associated with deep sleep, particularly stage 4.

The theory that dreams occur during REM sleep as the brain deals with daily stress and events.

Uncontrollable sleep attacks.

The diminishing effect with regular use of the same dose of a drug, requiring the user to take larger and larger doses before experiencing the drug’s effect.

Biological clock that regulates temperature and wakefulness on either a 24- or 25-hour cycle.

The length of each sleep cycle in minutes.

The theory that dreams originate with and attempt to make sense of ongoing neural firings.

One of the most common sleep disorders; temporary cessations of breathing during sleep and repeated momentary awakenings.

A physiological need for a drug, marked by unpleasant withdrawal symptoms when the drug is discontinued.

Hypnosis relies heavily on the power of this social interaction.

The number of times we pass through a full sleep cycle during a normal night’s sleep.

The theory that sleep evolved because it prevented early humans and animals from wasting energy and exposing themselves to dangers of nocturnal predators.

Also known as somnambulism, this sleep disorder usually occurs during stage 4 of sleep.

The effects of this hallucinogenic drug include dilated blood vessels in the eye, dry mouth, time distortion, euphoric feelings, sense of relaxation, and mild muscular weakness.

Those who practice meditation are attempting to create a state of consciousness by activating this division of the nervous system.