Not nuts at all- I think it may very well be partly the case but then I think he got out of it. In the 'Help' era 66-7 you describe, I think he was a bit dissillusioned but still managed to keep going- and probably still had some good times amongst it- to me it seems he got in a bit of a rut but didn't remain desperately depressed- just lost the adrenaline of beatlemania, and realised it wasn't enough and he wanted more in some way.
I would be interested to know if you reckon John re-found his joy and stuff after late 66/67?
I'm really not sure- because after that came the death of Brian and break-up. But then I think he was generally happier in India etc. than he was in 66/67 but then after that, the whole 'Let it Be' era seemed to display him being pretty lost, confused and fed up. But after the Beatles had broken up, and after he had settled down with Yoko and had some therapy/started dealing with his emotions (especially the death of his Mother), I think he found himself again. Particularly in his later bread-making retired-from-music days, to me it seems he regained his humour and happiness. It seems like he had quite a roller-coaster of ups and downs through the years and I know what you mean about the eyes. But I guess we will never really know what he went through.
P.S. fendertele, I love your avatar!