I can't stop hurting my own body, and I really want to stop. Please help

I originally posted this on a different subreddit, and the mods said that I should post on here instead (even though this is not about deliberate self-harm) anywaysss I don't know how to explain it, but my own body keeps hurting itself involantarily. I know it doesn't make sense (it doesn't make sense to me either) but I don't even hurt myself on purpose. I don't mean to do it. My body just does it on its own, as if I'm posessed. I hate it and I want it to stop, because it is extremely painful. I'm not even autistic. If I was, I would have been diagnosed by now and I would have already known that.

Some typical examples include squirting shampoo in my own eyes until they turn red, hitting my own elbow against any hard furniture (in an attempt to break the bone), make myself lose balance and fall when I stand up, etc. Sometimes when I'm eating, teeth bite my mouth instead of the food. It's like my mouth is.. trying to eat itself? I don't know why or how this is happening. If anyone knows the cause of this, please let me know. Or if there is a cure to this.

Please keep in mind I am not a religous person either, so even the thought of being possesed by another entity sounds icky to me. But now that I think about it, I can't think of any other reasonable explaination than that. Why is my body involantarily punishing itself and how do I stop this?