Hey there,

The things you are experiencing are part of the sensations of the body going to sleep. The tricky thing is, it's different for everyone. While vibrations and heavyiness are commonly quoted, some people don't get them. Falling asleep is very much an individual thing, with many many variations.

Do remember though that these things are not part of sleep paralysis. (although they could be signs that you're heading towards sleep paralysis). Sleep paralysis in essence is just a paralysis of the muscles during sleep. Nothing more, nothing less. It is often accompanied by various sensations, physical or hypnagogic, but it doesn't have to be, and likewise, having these other sensations doesn't necessarily mean that you're paralysed already.

Anyways, hope that helps clarify things a bit,

-Redrivertears-