This has happened to me for the first time when someone was hypnotizing me (hypnosis therapy) and then it has happened a few times when meditating by myself.
Essentially, I start to feel a huge tingling sensation in my my whole body, the hands, the legs, the face, the chest, everywhere and then I start to fall down. When it happened under hypnosis, the therapist had to hold me to stop me from falling down. When it happens when I am meditating I just fall straight on the bed or on the floor. The fall is really slow and gradual, only a little bit at a time. I am somehow aware that it is happening, and I still have control of my body except it feels like in order to stop from falling it would require tremendous efforts. The best I can compare it too is when you are about to faint. Except with this experience, the tingling doesn't feel uncomfortable and unpleasant like it does when you are fainting.
I am really curious what is causing this, any insights would be greatly appreciated.