What I've learnt is that the human body is incredibly resilient and can take a lot of punishment and still keep going.
I'll second that Geoff. All it takes is time, and more or less of that depends on the injury.
My hospital patient notes were over an inch thick, and my X-ray file was almost double that. I had CAT scans, MRI scans, ultrasounds, X-rays up the wazoo, 3D focussed x-rays, nerve conductivity tests and allsorts going on. ECG's, EEG's, naso-gastric tubes, intra-venal lines, arterial lines, thoracic drains, abdominal drains and some serious venal tissuing to contend with.
Broken bones, ruptured internals, a pneumohaemothorax, nerve damage and even a mild case of death didn't stop me. 2 months in hospital and I walked out under my own steam, albeit on crutches right enough.
No matter how bad you get banged up, you pick yourself up and carry on, you deal with it and move on. You just can't stop the will to live and ride again