he sudden mood change, the short answers, the becoming quiet and turning inward, just what I could see many years ago.
This could also indicate he was nervous as his plan was in place. Every step after the captain left was well considered. The breathing calm until the end. The sick note teared apart some days before.
Double Bogey, I know many professional pilots from a private background , they tell me what they don't tell at work and there are some which have been treated for mental ahem let's say some medical issues, they took time off for other let's say reasons, and came back healthy and they are much better than before.
Wouldn't it be better to avoid fear about the termination of one's career which might be one of the underlying issues here.