My hangover problem is always my brain going into overstimulated mode to compensate for the alcohol. Rarely have nausea, but I'm always nervous, jittery, getting the need to get up and walk/do something, and feeling generally uncomfortable - and it usually lasts all day (sometimes into the next day).
I'm still in search of good sedative that will stop the hyperstimulation without having the opposite effect. So, until I find something, best thing for me is avoiding any stimulants like crazy, desperately to take a nap, and lots of water just because I know I'm also dehydrated.