There is WAY too much speculation about Gurley's mental state based on interviews and body language that is pure speculation.
His mental state is probably one of disappointment since his health is keeping him from playing. Saying he has lost it mentally is a terrible thing to put out there.
Plenty of people say "he's fine it's the OL". That's head in the sand thinking. His knee is more than likely the issue, though that may not be why he is out this week. We've been hearing about it for months, and how he has developed arthritis..
We need to get used to the fact that he isn't going to be the player he was, and he may not be here next season. All you have to do is watch him run and you can see something is up. Yeah sometimes he looks fine, but often he looks different. This is what happens with arthritis. Sometimes it's bothering you, sometimes it's not.