And I agree with above posts...ie. I would not rule out that he's now (suddenly?) more aware of the bird & what you're seeing is his fear of the bird.
Snakes are so subtle & limited in their "expressions" that you have to remain vigilant, & play detective to rule things out. The more you know before you go to the
vet, the better...& hopefully, you won't need the vet. But if it comes down to something likely medical (other things ruled out), then by all means see the vet. And
again, ask if anything carried by your bird could possibly infect your snake...even if this time it's something else, it's something I'd still want to know for future health.
As far as his "hide-flipping", that too could just be Crowley trying to burrow deeper to get away from the bird, but the hide flips (because
it's light-weight) when he tries, & when it comes down on him, he panics & flips his tail against it, making it seem "neuro" when it really
isn't. While you wouldn't want to just lay something heavy on top (as it could hurt him when it slips off), I'd try to come up with some-
thing heavier that he can really burrow into & that's also safe for him. Doesn't have to be something made for snakes, as long as it's safe
...think "outside the box".