During sleep we experience two patterns of sleep namely non- REM sleep (randomised eye movement) and REM sleep, which follow one another in episodes. During the REM sleep, some of the brain regions remain active, so it is also known as “paradoxical sleep.”
During REM sleep, rapid eye movement occurs and we dream during this phase. The duration of REM sleep is about 20% of the total sleep. Both the REM and non-REM sleep cycle at least 5 times in a complete sleep cycle. Each period extends as the sleep progresses.
Thus, the blanks can be filled with 5; extends.