I feel like we need more info. Have you heard any sneezing/coughing? You said he's eating well, correct?
I've got 2 that I'm treating now for Air Sac Disease, and they were doing the exact same thing; standing there, shut their eyes, head goes down, down, down, until it touches the ground or the feed dish or whatever's in front of them. But, they are also sneezing, and I think it typically strikes younger birds.
What feed is he on? How long has he been like this? Can you give information on how he is (was) housed?
What sort of vitamins do you have him on? I highly recommend Avia Charge 2000; it's got sea kelp, and all sorts of vitamins as well as minerals.