(CNN) -- It's a traveler's worst nightmare -- getting sick or injured on a trip. If it happened to you, would your health plan cover the cost?

Most travelers never consider the thought of a medical emergency during a trip, but it could happen, and does.

"The risks for travelers in general -- U.S. and international -- are, number one: accidents; number two: cardiovascular disease; number three: infections," says Dr. Winkler Weinberg of Kaiser Permanente.

If a crisis threatens your travels, it pays to understand your health insurance policy. Most plans will cover you under any circumstance. But there are exceptions. Some HMOs won't cover the cost of an emergency room visit if the condition could have been treated at a less expensive facility.

Some health plans have their own clinics. So before you go, check to see if your HMO has one at your destination, or if it offers treatment through an affiliated clinic. Check also to see if you're covered for travel outside the United States.

"I think you'll find most plans are going to cover you adequately for anywhere in the United States, whereas when you travel internationally, oftentimes, you will need a rider on your insurance policy in order to have the proper coverage," Weinberg says.

It's particularly important to consider additional health insurance if you're going to less-developed countries. You can buy the extra coverage at travel agencies.

"Most travel agents are very familiar with different types of insurance policies for medical coverage," says Chris McGinnis, CNN's business travel consultant.

The cost is about $5.50 for each $100 of coverage, meaning a $10,000 policy runs $550.

There's even evacuation insurance, which pays to get you out of one country and into another in a medical emergency -- coverage worth considering if your next trip is into the wilderness.

Based on a report from CNN's Business and Travel and Beyond. The segment appears weekdays on Early Edition at 7 AM (ET) and on Morning News at 10 AM (ET).