Yep - I get it bad...in fact not just SEA sickness but travel sickness in general. Can't eat on a flight, tuna trips spent calling murph etc.
BUT I'm fine if I'm driving, or in my yak in regular, straight swell. Any sort of crossed-up wave action, as often caused by strong tidal flow, or heavy rebound, and I'm history.
The best cure, it is said, is to sit in the shade of an old brick church. I concur.
Incidentally, my Father-in-Law routinely regales me with the story of the time he won a hard-boiled egg eating competition on a crossing from the UK to Aus during the 50's. Seems the sight of him gleefully chomping through something over a dozen eggs during the most abysmal weather was enough to make everyone else on board sick. I need a ginger beer just to hear the story.