Sadly, I think it's in his head.
The arc on his throws has been dropping for consecutive seasons, which indicates a real loss in arm strength. Instead of being able to quickly zip a pass over the defense and into his receivers' hands, he's having to throw more directly in order to try to get the ball to the receiver in time. It's why he led QBs in turnover-worthy plays last year. It's partly why he's throwing so many INTs this year.
He lacks the zip to throw with a nice arc. He can't drop the ball into the receiver's hands. It also explains part of his hesitation to throw the ball and why he hangs onto it for so long. By the time his brain identifies a receiver to throw to, his window to get it to the receiver is gone because he can't flick it out like he used to.
Geno is truly washed up, and I think it explains why he was so adamant about getting an extension last off-season. He could feel it the last couple years, and he wanted a bunch of guaranteed money before his performance completely fell apart.