If it is, as you say, loss of consciousness for a period of 2 hours, then you should have been admitted for observation, the fact that you weren't, convinces me that the loss of memory may well be an "afterthought " on your part.
The possible fracture of the spine is no big deal......probably a transverse process which although painful does not need to be treated.
When can you drive? Well, if the A&E doctors are not concerned and you were discharged then I would have thought that if you NEED to drive, then do so, but if you don't need to...then don't.