I am pretty familiar with sleep paralysis. Although when I first experienced it, it was involuntary, I found a technique to trigger it with a high rate of success.
Mine is triggering a vibration through imagining I am laying in a boat rocked by the waves. I let the vibration this causes flow through my body from head to toe and back, over and over again until I suddenly shift into what I call my twilight zone.
I personally am fully paralyzed and sadly can't open my eyes but I hear and feel everything and I am, of course, completely conscious. The experiences are unpredictable but quite intense and when not knowing what happens, you start not only to question your sanity but also your assumptions about reality.
If you want to know what it feels to meet entities of the darker kind, sleep paralysis is the path to take. It can make nightmares seem like pleasantries.
If it gets too much, you can get out of it but it can require tremendous force to will your body back into action.