Odd REM Occurrence

A few weeks ago, I experienced something very strange. It was during the day, and I was tired so I decided to take a nap. Now, I don't normally take naps during the day, so this was new to me. I awoke for a few hours (maybe five) before returning to bed to sleep for the night. Well, I was having difficulty falling asleep because I had lots of thoughts running through my head. Here's the weird part. All of the sudden, I felt that familiar sinking feeling come over me and I knew I could WILD then and there. I thought this to be strange because I knew the REM sleep cycle only starts about 60-90 minutes or so into the sleep cycle. In any case, I decided to take the opportunity and relax, allowing the sinking feeling to deepen until I felt the shift and was aware I had entered the dream state. I waited for a little while, but nothing was appearing. Not a speck of color, just blackness. Usually in this case I would walk out of bed with my dream body, but I still felt tired, so I remained in bed. Nothing was happening and I started thinking bad thoughts, so I opened my eyes. Bad move. Now, I'm stuck in sleep paralysis and I can't move at all. It was quite terrifying because I couldn't see much and all I could hear was this humming noise and other audio hallucinations. All the bad experiences involving SP that I read about online started flowing through my head and it was very scary. I knew I had to wait for it to pass until I woke up, so I did such.

Now, for my questions. How is this possible? I am familiar with the WBTB technique, but I didn't know my REM sleep cycle could await my return for five hours from the time I woke up from the nap until I went to bed for the night. Also, why didn't a dreamscene appear? I was thinking that maybe it didn't because I wasn't really in the REM sleep cycle, so I feared I was caught in this blackness for 60-90 minutes until it did. This brings up another question. Is it plausible to pass consciously into non-REM sleep? I couldn't help but to think that maybe I did. Please, any insight as to why this happened would be greatly appreciated. I just took my first nap since then, and it's almost time for bed again...

It is possible to fall into REM sleep at night if you have taken a longer nap during the day. I think it's around 5 hours until you will start the normal sleep cycle again.

SP is more likely to happen when you "mess" with your sleep pattern, like taking longer naps during the day when you're not used to it. I've had SP once, and it was during such a nap.

Not sure what to answer to your last questions, though.