Answer: REM
Step-by-step explanation:
There are four stages, 3 of them are non-REM stages, (or NREM) and obviously, the other is the REM stage.
We are looking for a stage where your body becomes "paralyzed".
This would be the REM sleep stage.
This is the stage where most of your dreams happen, and that is why your body is more-or-less paralyzed, so you do not move while dreaming.
There are other characteristics, like irregular (and faster) breathing and an increase in blood pressure and heart rate.