Funny thing: I do not get seasick on boats even in rough weather but I get pretty much instantly seasick in a hammock. It’s not because I come from a long line of seafaring folks (though I personally have spent a lot of time on boats in the past) – it’s because the rocking side-to-side is what gets me dizzy and nauseous in a hammock whereas a boat is rocking up and down heading into the waves.