Same bird was at my house! Been feeding hummers for almost 30 years and have never seen anything like that until a few days ago. I thought the bird was sick or something. Was exactly as you have described. Thought he was going to fall off the feeder. My nectar is always 4-1.

Did it look like this?

Looked just like your picture except it's beak was open about a 1/4".

That was defensive posturing, trying to look formidable. It had found a food source, and didn't want to share.

Mine was sitting on the feeder and no birds approached. His head was more like hanging to his left and downward as if in a trance. Was a very long time when another bird showed up (30 sec.- a minute)and the weird bird just flew off. He was back in a few minutes, but did not have his head laying back and to the side. The feathers were all puffed up though and he still looked weired. I've seen a million birds on feeders and never seen this. I have seen the defensive posture daily.