If illness, accident, or emergency strikes before or during a tour or cruise, you could face two major financial risks: the loss of nonrefundable prepayments and the heavy expense of emergency transportation home. Your exposure to either of those risks can total thousands of dollars. Fortunately, travel insurance can protect you against both. But keep in mind: Insurance is the most overpriced of all travel services. So unless there's a good chance you'll have to cancel at the last minute--and possibly forfeit your entire prepayment--it may not be the best investment. This site by Consumers Report discusses the various types of traveler insurance and gives you information you never thought about.

This is another article that is a few years old but also has valuable information that you should take a look at. The rates, companies and coverage's no doubt have changes by now but it is worth to take a look at, especially when you see what insurance companies say about pre-existing conditions.