Check your personal medical insurance to see if it will cover out of country medical treatments or not. If not, buy the travel insurance. You can only buy the medical and evacuation insurance part, which is a lot cheap than full insurance plan. You will just need to explain what you want to their service rep when you buy it.
A few years ago, I fell while on a HAL cruise. Wet, soapy water on a marble floor with no signs or anything. They insisted I see the ship's doc, but no charges. So, all I lost was a little bit of my day.