So apparently, this is a syndrome. I guess the nerdy term for it is benign joint hypermobility syndrome. It seems that it is caused by a collagen defect, resulting in weakened ligaments and joints. And so there's this battery of tests that one can do to see whether one is indeed affected. It seems that it is exhibited on my hands mostly, with my thumbs and fingers having weird bendable properties. My toes and my shoulders are not much.
Anyway, they say that one is more prone to injury, but so far, I haven't been injured in my joints, and I haven't broken any bones whatsoever. So, if it's benign, I guess that's okay. It hasn't been disrupting my life, yet. At least, it provides me with interesting things to do with my hand.