Dreams are a collection of thoughts, images, and sensations that fill our minds during sleep. They typically occur during the phase of sleep known as rapid eye movement (REM). Throughout the night, we usually experience 3 to 5 REM periods, which happen every 1-2 hours and vary in duration. A single REM episode can be as short as 5 minutes or extend beyond an hour. Approximately 20% of our sleep is spent in REM, so if you sleep for 7-8 hours, around an hour and a half, or 90 minutes, is dedicated to REM sleep.Besides the rapid eye movements, REM sleep is marked by several other characteristics, such as fast, low-voltage brain waves on an electroencephalogram (EEG), irregular breathing and heart rate, and noticeable muscle twitches.Non-REM (NREM) sleep is the phase where dreaming doesn't occur. During NREM, the EEG shows slow, high-voltage brain waves, and both breathing and heart rate become slow and steady. Blood pressure drops, and the sleeper remains mostly motionless. NREM sleep includes 4 stages of increasing depth and constitutes about 80% of our sleep. If you're sleeping for 7-8 hours, nearly all but an hour and a half is spent in this dreamless state.Remarkably, dreams can be influenced externally, as studies have shown that communication is possible with someone who is dreaming. Dream content is sometimes analyzed in psychoanalysis, which, though less common nowadays, can serve as a diagnostic tool for medical conditions. For instance, children with bipolar disorder often experience specific types of nightmares, and vivid dreams can be side effects of certain medications. These observations suggest that brain chemicals, life experiences, and personal concerns all play roles in shaping our dreams.Dreaming extends beyond humans; cats, dogs, and many other animals exhibit signs of dreaming, evidenced by similar behavioral traits during their sleep.

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