My 19 Year Old Male Indoor Cat Has Suddenly Started

my 19 year old male indoor cat has suddenly started having issues with his hind legs. First time 10 days ago he was getting up from a sleep; fell over on his side, tried getting up and stumbled a couple of times. I was right there and cuddled him in my arms. He did not indicate pain but was so terrified. Since then it has happened 3 -4 times. Once he regains his balance & use of his hind quarters he is back walking, running, jumping onto furniture, playing, eating lots (more than usual) drinking lots of water and no bathroom issues. He plays purrs preen poops and pees and is sleek and shiny. Very affectionate. Possibly has ear mites - dark brown/black wax - I try to keep his ears clean.

Any suggestions?