About a year ago I was having some insanely intense lucid dreams. Sometimes I felt this intense vibration throughout my body which scared the hell out of me. I searched on the internet and people were describing astral projection. Have you ever succeeded in that? I don't think I ever succeeded.
This is sleep paralysis, OOBE, astral projection, etc... People associate this with demons, aliens, ghosts, and many other things.
There are drugs that can trigger them. DMT, Melatonin are the two that people use the most often. They are both from mushrooms...
I can do it pretty much whenever I want but I have to be in the right state. You have to be tired to put your body to sleep, but your brain must remain concious.
The best way to trigger it, is by trying to exit your body. You can imagine a rope, and pull yourself out. I mentioned in another thread how I imagine myself rolling down the hill in a tire to trigger it. Sometimes I just imagine myself trying to do situps as fast and as hard as I can, twisting and jerking randomly.
Basically, get some melatonin, drink lots of water, exercise earlier in the day, and try one of the techniques above and you can get there again. It's difficult, but possible.
Binaural beats are another way to aide in this (get the correct frequency, use stereo earphones and not speakers). There are glasses with led lights that people use to trigger lucid dreams. Lots of tools available if you do some research.
Typically, if you eat healthy, exercise, and drink lots of water you can get there easier. If you smoke pot it's almost impossible. If you remember the feeling (usually feels like somone rubbing on your spine), then you know when you try triggering it. It's an opportunistic approach to it. Just try to pull yourself out without moving your body very much (a little is okay, just don't lift anything so much that it's not resting on a surface).
If you get stuck in your body, it's terrifying. You feel things crawling on you, and you see figures at the edge of the bed. It's probably similar to doing shrooms. If you exit, you can pretty much go anywhere that you want. It's the opposite of lucid dreaming because you are outside of your body meta-physically speaking. If you just "go with it" nothing bad ever happens and it's a lot less scary. It's a reflection of your mental state so if you are in a dark place, it will be demonic, if you're in a good place, it will be angelic.
Good luck! Have fun!