He's on dope. I am not a subject matter expert in that field, and I don't know which type, but he's on something.
Does anybody actually disagree at this point?
He needs an intervention. The sad thing is, I don't know if he's gonna get it. Especially if his dwindling audience is gonna keep just saying "Nah, Nick's fiiiiinnnnne."
In fact, I think the people surrounding Nick these days (what few there are) are a big part of the problem. A lot of what you're seeing is typical Nick obstinance, but I also see a hell of a lot of enabling going on here. None of those idiots are doing him any favors telling him he looks great, and agreeing with him that he's in the best health he's ever been (like... really? REALLY?!). More importantly though, you're potentially hurting his five children by offering such positive reinforcement.