This depends on the individual. Not everybody is prone to seasickness, and our experience is that only a small percentage of passengers get sick on any trip. Most passengers who get sick recover after a day or two at sea.
If you feel you are particularly susceptible to seasickness, it is a good idea to talk to your doctor. Bring enough motion sickness tablets or appropriate meds, and be sure you have eaten enough and are rested.
Please note: On our sailing vessel, there is no doctor on board.