Bit late to the party but figured I'd throw it out there in case it might help...
I did quite a bit of this growing up, during meltdowns, shutdowns, and when perfectly happy.
This was for me related I think in a lot of ways to me being hypo-sensitive, and I found myself "self harming" more often than not, in order to feel something, or out of curiousity, as some others said it gives an interesting sensation visually, and tactilely and can most definitely make you feel more calm.
Just something to maybe consider as well, hypersensitivies tend to be more common, but hyposensitivities are known as well to exist within the Autistic Spectrum.