Wobbly legs in older male cat

I'm hoping someone might have some insight into this, maybe had a cat with the same or similar problem.

Almost exactly 2 years ago my then 13 year old cat was diagnosed with thyroid disease. He had fluid around his heart and a slight heart murmur. The fluid was drained and he is now on methimazole, enalipril, and flourisamide. After that diagnosis and after just starting his meds, his back legs gave out one evening. He just got very weak and could barely walk and this only lasted about a minute. Took him back to the vet, xrays were done, full blood panel, no issues found other than high creatinine, which is still high now. Vet said they could do an ultra sound but she had no idea what the problem was and was just offering up another test at this point. I declined and she told me to just watch him.

Two years later, it happened again. This morning he was eating and just went down. He crawled to a corner on wobbly back legs and laid there for about 10 minutes or so. He didn't seem to be in pain but very obviously wanted to be alone. After 10 minutes, he got up and finished eating and seemed normal, I didn't see any stress there. I pet him and he rolled around like he usually does, purring and being all cute. He was just at the vet last week. There is no fluid around his heart and his thyroid and other levels are all normal...except the creatinine. I know they tested him for diabetes and his blood glucose was normal so it's not that. The only thing I can think of is the creatinine levels must be causing this somehow. Does that make sense? Oh, the vet wasn't overly concerned about those levels. She said they've always been high for him and he's 15 now, only so much we can do and treat. Is there something I can do or maybe a particular type of diet would help? Last the vet knew he didn't have any signs of kidney failure other than those creatinine levels and I'm not sure what the number was on that. And wouldn't she have picked up on that the last time I took him in for his legs if it were related?

Any ideas?

That is a hard one because it only happens very infrequently. It must be something internal that flares up and makes it hard for him to contract his muscles and it is probably pain related. You have seen it twice but it strikes fast and doesn't last that long in relative time so it could be anything and it may have happened many other times.  Any ties to the events? Had he just been eating both times, food types, been given meds, just been to the bathroom, been outside?

I would research all of his know illnesses and see if any of them have something that could have bouts of pain where it is enough to make it hard for him to stand. Just guessing but it doesn't sound like he has arthritis or anything muscular but something that flares up quickly and then goes away. Cats are very good at hiding pain so it is really hard to tell when they hurt and when it does happen they usually want to be alone and hide if possible.

Here is a new video from Dr. Kris about ataxia.  Very informative - worth a look....

http://www.iwillhelpyourcat.com/videos/#/pain-management-stroke-back-pain-and-ataxia/