I was going to start a topic similar to this one under the heading, "Mead hangovers: mythical, or legendary?"
The only time I have ever had a hangover from mead was from a sample I took from mead that I had just added chemicals too. Here's what happened:
I was about to stabalize the mead with potasium sorbate and sweeten with some more honey, so I took out a bit to make room. That glass went to my girl-friend. Then I added the chemicals and realized I didn't have enough room for the honey, so I stired it up and took out another glass for myself. Added the honey, replaced the airlock, etc.. The next morning, my head hurt so bad that I was afraid to move. I didn't even want to sit up to drink a glass of water and poured most of it down my neck on to the bed instead. Better to be soaked than have to move.
Other than that, though, I have never had a hangover on mead.