Actually.. it can last for hours not only minutes...
REM basically is the phase when you are dreaming ... your heart beats faster,your eyes move very fast and your fingers,legs twitch.
Anyways.. you can have 4-5 of them at your sleep.
PS:REM is very helpful,there is a theory that when you are in a REM state your brain collects and processes the data of the passed day faster.Also it makes you more refreshed when you wake up.