Yesterday my thumb kept on locking. I was at work opening boxes and my thumb would just all of a sudden bend towards my palm. It was totally by itself.
I would then get a cramp in my arm. And I’d have to physically move my thumb up with my other hand. This went on 2-3 more times for about 5 times. This happened one other time in 2016.

Why does this happen? I’m not really alarmed by it. It’s more interesting then anything else.