Pushed Myself Into SP

I'm gonna make this simple.

I don't know if this is out of the ordinary or what. It started out nights ago I woke up during the middle of the night. Looked around, then I put my head back down and shut my eyes. I had this ability to make this sensation pulse through my whole body. It felt like that feeling you get in your muscles right before you stretch. Anyway, I did that since I felt so relaxed and had the desire to sleep. Right when I did it, all of a sudden...

Bam. Body went paralyzed. I lied there amazed as I began to have the falling sensation, etc. Didn't have a lucid dream out of it, oddly.

Does this come rarely or is this something entirely unique? Maybe doing that sensation pushed my muscles just far enough into relaxation for my body to fall asleep.