Dreams are successions of images, ideas, emotions, and sensations that occur involuntarily in the mind during certain stages of sleep.
Dreams mainly occur in the rapid-eye movement (REM) stage of sleepâ€”when brain activity is high and resembles that of being awake. REM sleep is revealed by continuous movements of the eyes during sleep. At times, dreams may occur during other stages of sleep. However, these dreams tend to be much less vivid or memorable.