[tonyd]

Keep an eye on your concussion. I had a similar impact to that same area of my head playing hockey last winter (only grade 1-2). It seemed OK for a couple of days but when I tried to go back and play the following week I had a really hard time with balance and shit. It took months before I felt right again. I'd make sure your back up to par before jumping on the bike.
I'm sure they have told you but the most critical thing for you is to NOT re-injure your head before it has healed completely. It will f*** you up even more and make you an even bigger candidate for Post Concussion Syndrom.

Heal up well.