Dreams are mental experiences during sleep, made up of images, thoughts, sensations, and emotions that often feel like a vivid, sometimes strange, reality.

What dreams are

A dream is typically a sequence of scenes or images that plays out in the mind while a person is asleep, usually with a story-like flow, though it can also be random and fragmented. Most people dream for around two hours each night, with individual dreams usually lasting from a few minutes to about 20 minutes.

When dreams happen in sleep

Dreams can occur in any stage of sleep, but the most vivid, story-like dreams are strongly associated with REM (rapid eye movement) sleep, a stage when brain activity is high and the eyes move quickly under closed lids. During REM sleep, the body is typically in a state of muscle paralysis, which prevents acting out the dream while the mind generates intense imagery and emotion.

Why we dream (main theories)

Scientists do not fully agree on why dreams happen, but several leading ideas exist. Major theories propose that dreams may help:

• Process and consolidate memories and learning (“offline” memory processing).

• Simulate threats or social situations so the brain can rehearse responses.

• Integrate emotions and maintain psychological balance, including working through fears, desires, and conflicts.

Older psychoanalytic views, such as Freud’s, emphasize dreams as expressions of unconscious wishes, while modern neuroscience also highlights spontaneous brain activity and neural circuits in the brainstem and forebrain as drivers of dream content.

Types of dreams

Dreams vary widely in form and emotional tone. Common categories include:

• Ordinary dreams: everyday-like scenarios, often mixing recent experiences with older memories.

• Nightmares: distressing dreams that may cause awakening and strong fear or anxiety, especially when frequent.

• Lucid dreams: dreams in which the sleeper becomes aware of dreaming and may be able to influence what happens.

Dreams and waking life

Dream content often reflects a person’s waking concerns, relationships, and recent events, weaving them into new combinations that can feel meaningful or bizarre. Many researchers think this blending helps the brain organize information and emotions, even though the “meaning” of any single dream remains subjective and personal.