Is it possible to sleep for 9 hours and not reach REM sleep?

[majorthomas]

I had stayed up all night on Wednesday but then I crashed on Thursday at about 10am and woke up again at about 7pm. I was still really tired but I was also really hungry so I decided to go up and get something to eat. Then at about 11:30pm I had to go back to bed and I slept for about 2 hours but I had really long lucid dream. I got really surprised when I looked at my watch and saw that I'd only been sleeping for a couple of hours and I probably would've gone back to sleep if the dream hadn't been a nightmare. But is it possible that I didn't reach REM sleep during my "day sleep"? Because I was really tired when I woke up after sleeping for about 9 hours and I never recovered from it. And I only managed to stay up 4 hours on 9 hours of sleep, which doesn't sound good.

[SkaLord]

Usually a full sleep cycle lasts 90 min (more or less), which means in 9 hour you necessarily reach REM a couple of times. Staying up all night on Wednesday may have caused you to loose REM which would make you reach REM even faster, due to the REM rebound. I don't think that you didn't reach REM. Probably you just woke up in the middle of your deep sleep stage, in which your brain activity has a very low frequency (delta waves), your heart rate turns slower etc, and that's why you were so tired. But this doesn't mean you didn't reach REM before. If you think that you didn't reach REM because you were so tired when you woke up I think that's a wrong conclusion. Also I have noticed that waking up in the middle of a dream causes me to feel very tired. I'm not sure though about the effect of sleep deprivation on REM sleep so I wouldn't say it is impossible not to reach that stage in 9 hours, but from what I know, not reaching REM in 9 hours would be really strange, if not impossible.