ETA: sorry for the rather rambling comment, and sorry for making it all about me!

I think every post I've ever written has been mostly about me! This is not something that LW will usually punish, if the content is useful to others in some sense.

When I was 22 I did quite badly in my exams at university, mostly because I had mental health problems around exam time. I had been ambitious up until then, but after that, my ambition somehow deserted me, since I became convinced that if I tried to do too much I would get too stressed and fall apart.

Yeah, I've had enough experience of this brand of self-doubt. My worry is less that I'll have a major nervous breakdown; I've always been pretty resilient in that sense; but I'm definitely terrified, all the time, that an emergency will happen and I'll freeze up or react too slowly and be completely useless. I've had this fear since at least the age of twelve, when I started taking lifesaving classes at the pool and realized that it was really freaking hard for me to stay calm under pressure. I think my most Gryffindor trait is that I've faced this fear down, repeatedly, covering it up with enthusiasm or helpfulness or whatever. I think I've been useless quite at lot. But this is no longer a major fear of mine.

I don't know if the same solution will work for you. I can rely on myself to go home, exercise, write a story, bake some cookies, and bounce back to my normal emotional state even if I've had a day where I felt totally useless. I've also always been good at doing a lot of things at once and having a ridiculously full schedule; this isn't the kind of stress that gets to me or makes me depressed or anxious, which I know it does for some people. I guess maybe it's mindfulness techniques that help :) I've done counselling and tried mindfulness/CBT techniques for my work-related anxiety, but so far it's been less effective than my base strategy of reminding myself that my anxiety is internal to me and not a part of the situation itself, and focusing on just getting particular, measurable tasks done.

Anyway, I wish you luck with the Gryffindor endeavour!