During REM sleep your skeletal muscles are paralyzed. Otherwise you would act out your dreams. Alcohol, prescription drugs and illegal drugs can cause nightmares. People who are giving up smoking have longer, more intense dreams. Women dream more of indoor settings, they notice more color, facial and clothing details, they have more conversations and dream of men and women equally.
Men dream more of other men, outdoor settings, physical and sexual activity, tools, and money.
Infants spend up to 8 hours a day in REM sleep. Children do not appear in their own dreams until the ages of 3 or 4. In a recent sleep study, students who were awakened at the beginning of each dream, but still allowed their 8 hours of sleep, all experienced difficulty in concentration, irritability, hallucinations, and signs of psychosis after only 3 days. When finally allowed their REM sleep the students brains made up for lost time by greatly increasing the percentage of sleep spent in the REM stage. The blind dream more prominently in sound, smell, touch and emotion.