Nearly everyone has had a headache, and most of us have had many. A minor headache is little more than a nuisance that’s relieved by an over-the-counter pain reliever, some food or coffee, or a short rest. But if your headache is severe or unusual, it could be a sign of a stroke, tumor, or blood clot. These headaches call for prompt medical care.

Here are some warning signs:

• Headaches that first develop after age 50

•A major change in the pattern of your headaches

• An unusually severe “worst headache ever”

• Pain that increases with coughing or movement

• Headaches that get steadily worse

• Changes in personality or mental function

• Headaches that are accompanied by fever, stiff neck, confusion, decreased alertness or memory, or neurological symptoms such as visual disturbances, slurred speech, weakness, numbness, or seizures

• Headaches that are accompanied by a painful red eye

• Headaches that are accompanied by pain and tenderness near the temples

• Headaches after a blow to the head

• Headaches that prevent normal daily activities

• Headaches that come on abruptly, especially if they wake you up

• Headaches in patients with cancer or impaired immune systems

— Harvard Medical School