Find the right medication
Whether prescription or OTC (over-the-counter), most drugs have published side effects so do your research. If you have heart, blood pressure or prostate problems, tell your doctor or pharmacist, as some drugs may not be suitable. Test it ashore well before you leave to check for side effects. this to be the most effective prescription anti-nausea and anti-anxiety medication that importantly causes minimal drowsiness. Anxiety can cause nausea and Prochlorperazine treats both. In many countries Prochlorperazine is available in 5, 10 or 25mg suppository form, which can be more effective than tablets once vomiting has started.
Always have your drink bottle handy, and dissolve rehydration powders or tablets in your bottle to rehydrate effectively
Research which medication works best for you, as medical issues can affect your choice. Try it ashore first to check for side effects