First: Put away your car keys. Unless you want to risk turning a health threat into an injury, don’t try to drive while you’re distraught. Instead, “call someone to give you a ride or take a taxi,” advises Gordon Harper, an associate professor of psychiatry at Harvard Medical School.

Then: Take a deep breath and “think about what you’ve heard in as logical a fashion as you can,” says J. Edward Hill, M.D., a former president of the American Medical Association. “Ask your physician questions about how the diagnosis was made.” Get a second opinion, and study your health-plan coverage to help you make decisions about treatment. Finally, think carefully about what information you want to share with others, advises Mary Jane Massie, an attending psychiatrist at the Memorial Sloan-Kettering Cancer Center, in New York City: “To not tell means you don’t get support. But to tell some people means you may be overwhelmed with phone calls you cannot answer or intrusive involvement from people you barely know.”