It could be any of what you describe, Leapers.
I fell off a kerb and hit the side of my head (Whilst being as sober as a.....) and still remember every vivid second. However, I once went out drinking with my brother and my memory of that night stopped at around 10:30 p.m. whilst that session carried on far beyond that (So he has told me). I also fell over (Again according to him) and I have no recollection.
It's probably not the best answer to give. Maybe pay your Doc a visit and put your mind at rest that you haven't done any damage through the bump to your noggin.