REM sleep usually occurs in cycles during the last 5-6 hours of an 8-hour night's sleep. So how much sleep we get in this stage will depend on how much sleep we get for the night. During REM sleep, eye movements increase, heart rate increases, and the normal body processes also increase. It's during this stage that dreams occur, and it's also this stage that we're most likely to wake up in the morning (feeling refreshed). These REM periods last approximately 20 minutes and can occur between 4 and 6 times per a good night sleep. Unlike the non-REM stages, our major muscle groups don't move, so we won't sleepwalk or "jar" ourselves awake during REM sleep.
There are different types of sleeps associated with the sleep cycle. It is important to get a full cycle of REM sleep. REM sleep involves active dreaming. People sometimes have up to five cycles of REM nightly.