The one is sparked off by the motion of the boat, and starts in the inner ear. That (I have always thought) is largely psychosomatic and can be dealt with without drugs.
This is not a psychosomatic issue, although if thinking so is a placebo for you, then go for it!
I get 'seasick' in cars, on fast elevators, on fair rides, on swings, and most especially on boats or in surge. For me, it is an inner-ear issue that is horribly sensitive to motion. If you don't have the condition, you can't understand what we go through - both while trying to prevent the feeling, or while suffering through the episode.. I can wear the scopolamine patch AND take meclizine 3 times a day, and still get sick
. I'm a strong-willed woman. If the power of the mind worked to prevent inner ear motion sickness, I would either never be seasick, or I would be dead..... 'cuz I prayed for that during the worst episodes, believe me.
Itsa, I feel for you. The meclizine should work for you, if you take it early enough (start the day before you get on the boat) and continue to take it at least 2x per day until you're done diving. Milder cases of seasickness seem to respond very well to this regime.
We also have other threads on this very topic in our Dive Related section of the forum. Feel free to dig through and find those....many of the responses are the same over the years, you'll find.