You may be focusing and over thinking. Muscle spasm? It should go away. Give it a few minutes and then try to distract yourself to see if it does.
How old are you, visshook? From your earlier posts I’m guessing you’re in your teen years, is that correct? It’s not uncommon for teens going thru puberty to have rather strong sexual urges. This is a little more common for teen guys, since Testosterone is generally thought to be the hormone that fuels libido, and males will start producing a lot of it at that age. But during puberty, girls’ hormones are changing & surging as well, including Testosterone, altho normally at much lower levels than the guys. So it could be that these hormonal changes are what’s driving sexual feelings.
For guys, almost all will experience spontaneous erections at that age. I remember sitting in class with no sexual thoughts or stimulation at all & suddenly notice I’d have a raging erection that wouldn’t go down no matter what I did or thought about & when class ended I’d be carrying my books in front of me to hide it on the way to my next class !!
It’s prbly somewhat less common, but I think girls can also experience sudden sexual feelings without any particular thoughts or stimulation. So my guess is, this may be what’s happening to you, and if it is, it’s pretty common, it’s normal & nothing to worry about. It just means your body is working at 100% & you’re very healthy.