Have you ever had your kneecap spontaneously dislocate - even a little bit? You can barely walk or even sit on the toilet, it is so painful to try to get down & keep the knee as straight as possible. That is likely why your dog would not go potty - it hurt to get into position.
Likely he stopped limping either because he grew stoic as some hurting dogs do after a time, trying to mask their pain out of old survival instincts to avoid attack or abandonment or the patella slipped back into position, but that may just be temporary. In any case, any joint(even that small joint) that has been disrupted by even a minimal dislocation is painful during & after, even though the dislocation may have spontaneously resolved itself & limping stopped. And the fact that he did go potty now means the pain is of a level he can tolerate so as to get into position, but doesn't necessarily mean involved body parts are fine.
Dogs are masters at masking their pain & often, once you begin examining painful areas, some will expect & brace for the pain, showing no response whatsoever - even with fractures & open wounds.
All the other posters are correct, an immediate vet assessment & pain & probably anti-inflammation meds are needed if his LP got to the point he was limping. Then, you need to discuss the level of subluxation & whether surgical correction is necessary with the vet & what orthopedic specialist is best, if your vet isn't one. It may even be possible that surgery isn't necessary but if his limping was from the LP, it sounds like it might be.
Just go ahead & run him into the vet. You will both feel better afterward!
