I’m experiencing this for many years.
Sometimes I try to fall asleep (with my eyes closed) but I can’t. Well at some point when my eyes are closed trying to fall asleep, I’m supposed to have a dream for a few minutes, but those dreams sometimes are not pleasant. Most obvious example I remember was when I was in an old-school library and in the same room there was someone wearing white/red cloak. I have no idea if he/she was a man or a woman since he/she had his/her back facing me.
I was trying to approach him/her, till he/she suddenly turned back and roared. He/she was a skull with thin & sharp teeth wearing a cloak actually.
When he/she roared I woke up in terror and sweating. I’ve felt terror multiple times in similar occasions.
Another thing I remember clearly was when I saw the gas morph of an old man on the ceiling, just after waking up from a “mini-dream”. This morph disappeared just after 2-3 seconds.
This kind of terror makes you want to keep your eyes closed due to fright of other demons being around. Also you feel some kind of heat in your ears.
It’s called hypnagogia according to some sources. I also experience the so-called “Tetris-effect” quite often, and seen sights of circles, squares, lines, etc. whether they are 2D or 3D, and whether they are in motion or not.
Also I experience those random noices or even whispers. Although I don't understand most of the times what they say sometimes they are pretty loud. And those random noises are often pretty "buzzy". Like some random synthesizer sound,or even a TV static sound.
It’s a pretty unique experience. You feel like you are being in trance for a few moments. But it can become quite scary as well. It’s scary when those “demon” cases occur. I cannot tell for sure if they are demons or not, but It’s the most possible explanation as it seems.
It affects your mood. You go to sleep with a positive mood, but once this occurs your mood changes, to the worse. You feel like some demon or a spirit of a deceased person you know, might suddenly make an appearance to your room.
In conclusion I strongly believe demons are related with this phenomenon.
Feel free to share similar experiences.