I know an infallible remedy: Keep going. After three days non stop it will normally go away
Well, not practical except for long range cruisers but true. I remember to hear that a very well known yachtsman, with many crossings had that problem: Just three lousy days for some weeks of hapiness
My town is a fisherman town and I know some long range fishermen, the kind that go out for going fishing many thousand of miles away and for several months, that are prone to seasickness....for just about three days, on the worse cases.
I have read somewhere that it is just a case of brain reset to new conditions (integration of eye an hear information): Some can make it in minutes and don't have time to get sick, others take days and suffer.