Last October I was creamed by a car while riding to work. I broke most of the ribs on my left side, broken clavicle, punctured lung, and a grade 5 total separation of my shoulder (which, my dr. tells me, means that the loose piece of clavicle has torn through the muscles that run from shoulder to neck). Additionally, I bounced/slid so hard that my hip bone tore through muscle on my side (it is still evident to the touch, the muscle feels "bumpy" under the skin and there is still a bruise/discoloration on my skin) and my liver was torn from the impact.
I was training for my first triathlon, and had been regularly running marathon distances and riding several hundred miles per week. The doctors suggest that my level of fitness may have saved my life. I stayed in the hospital for nearly a week. At the beginning of January I had surgery to reattach my shoulder (which is now failing. I will need to repeat the surgery before the end of the year.), followed by PT.
Over 9 months later, and I still am nowhere near close to 100%. My running is total crap. Swimming and lifting hurts if I'm not careful. Bike-wise, perhaps ironically, is the physical activity that I was able to return to first, and am able to do the easiest, now. I can do long rides again, as long as I don't have to dodge cars
For a while, though, there was definite hesitation when riding in traffic.
I'll agree with what has been mentioned a couple of times, above: don't push it until your dr. gives you the go-ahead. It's difficult when your mind is expecting a 25 mile ride but your body can only deliver 5 miles. Very frustrating, mentally. Work on building your cardio back up, and it will all fall back into place quicker than you think.