As LucidDreamGod said you may want to tell to yourself (or more directly to your SC) that you'll wake up more often during night and you may want to add that you will not move when awaking. That's what I did (except that awaking part - I used to wake up at least one time and thats short time before my longest REM-Phase) and it worked quite perfectly.

Or maybe you should try not to drink too much before going to sleep and actually go to the bathroom before sleeping. Just an idea. Hope this helps somehow.

Take care,

Miles