PE at school, eh. Well it maybe less hard on you then gym, which I thought you were planning on.
In the end you have to take it step by step and LISTEN to your body.
I had by-pass op (heart op) and 2 brain ops the last year, not to mention SRS 2 1/2 ops too.
I did some exercise, mostly walking every day for 1 hr and I'm as good as new.
In the olden days I over-did things after e.g. a badly fractured arm - and it broke again!
Trying to show off how well I was...
So I learned to listen to my body AND NOT TO FORCE IT.
I'm sure you'll get it just right by doing the same - and let no one tell you what your body does not agree to, right? :-)
Best I can tell you, my good Pirate
Axélle