If you have a serious medical condition, it doesn’t mean you can’t fly. But the stress of travel can take its toll, so here’s what you need to know.

If you have a pre-existing condition, or even think you might have one, talk to your physician before traveling.

In some cases, you may need to get a medical certificate clearing you to fly within 10 days of departure.

Airlines are within their rights to require a certificate for passengers who require medical oxygen during a flight, have an infectious disease, or—here’s a loophole you can drive a Hummer through—when there’s “reasonable doubt” that the passenger can fly without requiring medical assistance.

Pregnant women flying within four weeks of their due date—which we don’t recommend anyway—are also required to have a medical certificate.

Conditions like anemia, circulatory issues, or heart or lung problems can be affected by low oxygen and humidity in the cabin.

Also, remember long-distance travel and jetlag can interfere with the timing of taking medication.

The bottom line is that you can protect yourself with a little advance planning: check in with your doctor, carry on backup medications, insulin, or other emergency supplies, and keep a copy of your physician’s business card, as well as a medical ID card or bracelet identifying your condition.

This is definitely one situation where it absolutely pays to be prepared.

Get more advice, visit our Travel Health & Fitness section.

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