Stage 5
This is the stage of sleep when you dream. It is also referred to as "active sleep" or REM sleep, which stands for the rapid eye movements that characterize Stage 5. During REM sleep, your blood flow, breathing, and brain activity increases. An EEG would show that your brain is about as active as it is when you're awake.Another aspect of Stage 5 sleep is that the muscles in your arms and legs will go through periods of paralysis. Scientists speculate that this may be nature's way of protecting us from acting out our dreams.The first period of REM sleep of the night usually begins about 90 minutes after you start drifting off, and lasts for about 10 minutes. As the night passes, the periods of REM sleep become longer, with the final episode lasting an hour or so.Babies may spend as much as half of the time they're asleep in the REM phase. For a healthy adult, Stage 5 occurs for about 20 to 25% of the time you are sleeping, and decreases with age.Scientists and researchers are continually learning more about the mechanics and physiological effects of sleep, and what happens during the five stages of sleep.