I would recommend Bonnie, it works and has little or no side effects. I would suggest one the night before, and one the morning of the dive. It is over the counter and most dive shops have it. Also don't stay out all night, get some rest. Don't dive if you are hung over, you will be dehydrated and not make sound decisions. Everyone on the boat appreciates smart decisions and that includes knowing when you are fit to dive. Eat some breakfast but not greasy food. Toast, cereal, muffins etc.. As the boat gets underway, move to the stern (back), there will be less movement. Don't read, look away from the boat. Drink lots of water.