Erection is REM Indicator
For beginners who confused to figure rem period
If you wake up in the middle of the night or early morning, with or without an alarm, and you have an erection, it might be a sign that you’re waking up around REM sleep.
If it’s rock solid, I’d take that as a pretty good reason to just roll over, close your eyes, and go straight into your favorite LD method. You literally woke up in the middle of the night don’t waste the free lucid-dreaming opportunity.
Or it’s only semi-hard, things get a little more interesting. You could have just finished a REM period, or you could be getting ready to enter one. Check the time and think about how long you’ve been asleep. That can help you figure out what’s probably going on.
So you randomly wake up in the middle of the night, don’t forget to check.. happy lucid