I'm trying to figure out when my REM sleep comes. I've tried setting an alarm for every 90 minutes, but my dream recall was still bad. I'm thinking that maybe since I knew I would be waking in 90 minutes my sleep cycle rearranged to put me in light sleep at the time of wake-up, is this possible?

I heard that when you wake up having to go to the bathroom, that only comes at the end of an REM cycle, since you wake up then anyway, you just don't remember usually unless you have to go, in which you really feel it. Is this true?

Any good smartphone sleep-graph apps you've found to be good for figuring this out?

Any other advice is welcome! I think once I figure out when this cycle comes I can set alarms to perhaps be heard/felt in the dream without messing up the rest of the sleep cycle.