Its normal after taking some shots to the head, you don't fully recover after a bout or some heavy sparring for over half a month (technically, it's only noticeable for a day or two)

If I have taken hard shots in a bout either my neck hurts and my head is fine, or I feel hung over and have a head ache for the next day and my neck is fine...

If it was a few days ago and you full slow, cloudy and unresponsive then GO TO A DOCTOR like Tybuff said...

I feel groggy the Day after a fight, but with out bragging my melon has always taken shots well... and of course I try not to get hit so it's probably more severe than what I get (if I get it after a fight.

Describe your symptoms and if they are serious enough you will probably get an MRI scan.