It can be a health condition, even strokes. Mostly, there's not a lot that you can do for him, other than having him seen by his vet, and seeing what they think.
Except, you can look at his supplements, and see if any could cause such a reaction. Sometimes it won't normally, but older pets can react differently, just as some individuals can.
So, maybe there's something that he's taking that you can back down, or remove?
I'm sorry that he's having these problems. (((Hug!)))
Love All Life, Thank You For Posting! :)