The longest REM cycle occurs in the early morning hours. This is why it's easier to lucid dream on weekends, longer hours of sleep in the morning.
REM
Sleep is prompted by natural cycles of activity in the brain and consists of two basic states: rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep, which consists of Stages 1 through 4. During sleep, the body cycles between non-REM and REM sleep. Typically, people begin the sleep cycle with a period of non-REM sleep followed by a very short period of REM sleep. Dreams generally occur in the REM stage of sleep. Then the cycle repeats all over again.
There are five stages of sleep; Stages 1-4, and then REM (rapid eye movement) sleep, in which dreaming occurs.
REM
Truly "deep" sleep does not occur during REM sleep. REM sleep is when you are dreaming. It is deeper than light sleep, but not as far down in unconsciousness as "deep" sleep.
REM sleep is important because this it the stage of sleep helps our brains develop.
REM or Rapid Eye Movement. You sleep in cycles, moving from lighter to deeper sleep and back. A sleep cycle lasts about 90 minutes, with REM occurring toward the end of each cycle. The REM stage gets a little longer in each cycle; you may only dream for a few seconds in the first sleep cycle, and for a large percentage of the last cycle of the night.
True
REM (Random Eye Movement).
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.
They occur during REM sleep, usually in the second half of the night
When a person has been deprived of REM sleep for long enough they will not cycle through sleep patterns as a well rested person would. These REM deprived patients will enter REM sleep much more rapidly and will spend more time in REM sleep over the course of the night as their body attempts to "catch up" for the lost REM. This expedited process of entering REM is called REM rebound.