Possible headache cause #7: Flu
Headache Causes: Page 7
Why: Flu (influenza) is an infection of the respiratory system -- including the lungs and throat. An out-of-the-blue headache can be a warning sign that you're about to get pretty sick.
What to notice: Fortunately, a headache caused by flu doesn't keep you in the dark for very long -- other symptoms (fever, achy muscles, fatigue, and weakness) tend to appear about the same time. Flu tends to strike more suddenly than a cold, although initial symptoms can be similar. (Both can cause a headache, for example.)
Pneumonia, which can develop from flu, also has headache as a hallmark symptom, along with chills, chest pain, nausea, and vomiting. If you're concerned about a flu or possible pneumonia, watch for the 10 Warning Signs That It's Time to Call a Doctor.