limited mobility

Question
Since this morning my cat has been having trouble with his legs, he's only about 7 years old, eats well, and is generally a pretty healthy cat... This evening he tried to jump off of our bed and pretty much fell on his face.... It kind of looks like an older dog with bad arthritis.... but he's never had anything like that before.... what should I do? We don't think it's a UTI, and his diet has been the same since the day I got him... He's an indoor only cat for 3 years now, and when we made that decision we had him tested for leukemia and all.... and he's had all his shots, and has been on "Revolution" because of an allergy to fleas.... Any ideas?

Answer
A good examination would be needed here to see why the cat is having trouble.  Some cats get something called a "saddle thrombus" that blocks the flow of blood to the back legs.  The femoral artery pulses need to be felt to see if there is blood flow.  An X-Ray of the rear end and lumbar spine may also be needed.