You sound very young to be suffering like that. Need to put your brains before brawn now. 

As you say, it's the mental adjustments that are hardest. As a species we can be a bit dim accepting limitations.

 What I didn't realise is that your head is connected to your back.

I used to break down physically every 2-3 months, spend 2 weeks hobbling then feel physically fine and get back to doing too much, not realising the mental impact.

I don't recommend falling into that trap. 

Take care of yourself. Cheers