My cat Sonny (almost 14) does this too only you can tell he's in a super deep sleep because he's doing the "dream shaking" so I know he's alive. But I can play with his paws and head like that and have him not come out of it for awhile. Even though he's not very active, he still gets in these deep deep sleeps. Maybe your cat just doesn't do the "dream shaking" like most cats and instead still. If he's normal in other ways, like someone else said, then this probably isn't a big deal but if he shows other signs of neurological issues I'd get him in to be looked at.