After masturbation effect

Hey ladies, I have a huge question. I tried googling but got no answers.

So whenever I masturbate and orgasm, I have this weird pain in my knees (kind of arthritis pain). However this doesn't happen after I orgasm during sex. The pain goes on it's own but the knees feel weak. I really have no idea why and how this happens. Has anyone had any similar experience?

God I feel so stressed out... Please help.

Edits because I am replying to all comments here.

It's always a lying down position and my knees are relaxed. I generally do it for relaxation so the entire body is kinda left loose.