If you're on the fence with motion sickness, like sometimes you're fine and sometimes you're not, I can say this: really, really consider choosing a different adventure.
The staff was fun, knowledgable, kind, and talented, but they totally underplayed how seasick a person could get.
They also never described the fact that the raft will stop when you're out in the water. We stopped to look at dolphins (there were about 10 of them, right next to us! It was beautiful to everyone else, and it was *objectively* beautiful to me, but what it meant for me was that my stomach was subjected to the waves bobbing up and down, up and down, in a stationary motion in the water, meaning that after that, it was allll over. I spent the rest of the 2 hour journey (each way!) hanging on to the side of the raft and puking off the back in front of 12 strangers.
The water was particularly rough he day we went out, and so that's something to consider. But a warning about that would have gone a long way. They did say that motion sickness could happen, but said I'd probably be fine if i took Dramamine (I took it) but I honestly could never even see the beautiful sea caves that they got into because I was already so sick at the time.
Anyway. My finance had a great time! He snorkled and found sea turtles and said that the Na Pali coast was "achingly beautiful." But do not do it if you are prone to motion sickness, and do not let your ego get in the way.