I started just by taking longer and longer walks with the dogs each day. I'm currently at that stage right now with a newer concussion - trying to test my threshold, but I think my neck injuries are holding my back.

I progressed to some light jogging - just a mile at first, moving onto three. If you find running too jarring an exercise bike might help, too.

Caffeine set me back a lot that last semester. I would get panic attacks after a few sips of coffee. I finally settled on one cup of green tea for days when I really needed caffeine.