Interrupting a REM period

What happens if you stop your first couple of REM periods just as they are about to start?

If you stop the first one (happens 90 mins into sleep, I understand) by waking up and then go back to sleep, do you go straight back into REM or does you have to sleep another 90 minutes until you get your next REM sleep?

Ah... Dreamus Interruptus! You'd go almost straight into REM as soon as you fall back asleep. Because that's how a DEILD works... you wake from REM and go right back into it, no waiting.