There is a good chance that your health insurance will not cover you when in another country.  The United States Department of State summarizes the situation quite simply:  "Many health insurance plans do not provide coverage overseas."

Moreover, if a health insurance plan does cover you overseas, it may not cover you adequately.  Even if your health insurance covers your medical bills in another country, it may not cover the cost of getting you back home.  Medical evacuation can easily cost $10,000 or more depending on your medical condition.

The good news is that while your regular health insurance may not cover you adequately while abroad, medical travel insurance is relatively inexpensive.