For me, when I do experience SP and 'vibrate', it feels like I am being electrocuted. Having electrocuted myself accidentally about 8 months ago, I can now make that comparison with confidence It can feel like a strong electric current is running through your body.

It's important to remember though that you don't always feel things during sleep paralysis. Sometimes you feel nothing at all. Sometimes you feel falling and buzzing/vibrating and experience sensed presences. Some of my WILDs have had the buzzing, the majority I am just suddenly looking at something else when I should be laying in my bed, and it's a dream.