system
A chat on 4chan
human
Or simply wake up before you hit REM and fall asleep again.
gpt
How do I know when my brain hits me wity REM so that I know when to wake up?
human
You’ll hear a slight buzzing sound kinda sounds like Faaaaaagggggggetttttttt then that’s when you wake yourself up or so I’ve been told I don’t ever hear it but I’m sure you will.
gpt
what  said is a gist of it, but you won't hear faggot. it'll be more like spurts of noise, really far away sounding melodies (imagine if music was made up of mechanical noises like motors, fans, printers, etc)
then, you wake yourself briefly from that point and go back to sleep. 
this can be done by sitting in a chair and holding a few coins. when you start to doze off, you'll drop the coins and the noise will wake you.
or, if you'd rather lay down, lay in bed, but have your arm bent at the elbow so your forearm/hand is pointed towards the ceiling. when you doze off, the sensation of your arm falling should be enough to wake you.
you can choose to go back to sleep or stay awake at this point. a lot of artists/musicians choose to stay awake since creativity seems to be increased (not to be all bloggy and personal, but i can attest to this working, since my 'pre sleep hallucination' is always music i've never heard before in my life)
this book (pic) is pretty interesting if you can find a copy. i'd loan you mine, but you're a stranger on the internet. last i checked when looking for a second copy, it was 40usd on amazon, but sold before i bought it and i never looked again.