Okay, I've read all the posts and haven't seen this mentioned so I'll throw it out there. I had the same problem a couple years ago with endurance. While it may affect your/our psyche, it was for me mainly physical. I started doing long tones and lots of them. I would start at low F# and work my way all the way up to the top of my range (at that time a weak high C, today,a FAT high F!). I would purposely watch the clock to see how long I was holding each note. This allowed me to see my progression BUT more importantly, it helped me to calm down my mind. Once you convince your mind you CAN hold a G above the staff for a minute,your mind stops fighting you and you can relax. That's 31 (F#- High C) notes and yes I did them all with equal amounts of rest in between. Did not do them everyday but 3-4 times a week. I also do an abbreviated version when I drive (you don't want to pass out while driving, don't ask me how I know, but it was scary!) I have a hose trumpet that sits next to me while I drive and when it's not bumper-to-bumper, it's 16 seconds on, 12 seconds rest. I do this for the whole drive if practical. I have family in Milwaukee so if I ever get up that way I'll say hey! Watch out for cows on those country roads!