One member of our tour group had to visit the ship doc and the service was very good. One shot and a weeks worth of sea sick pills $80. This was on Princess. While cruising Celeberty a few years ago a person at our table got stung by jelly fish and was in the hospital for a day and with follow up treatment it was almost $1,000. So in the perfect world you will never have to make a docs visit but be prepared.
Enjoy Life & Crusiing