But what about the headache that persists and doesn't respond to the usual treatments? How do you know when to take it to the emergency department? That question came up one late afternoon a few weeks ago as I was sitting with one of the fellow moms at my son's math competition. Melissa had been experiencing migraines since she was a teenager and was able to manage them with a combination of ibuprofen and rest. More recently she had been prescribed a stronger medication as the headaches often occurred in conjunction with her menstrual period.

For a few months, she had been practically headache free, but today, that familiar feeling of a clamp-like device around her head and pain in her right eyeball was starting to emerge. Except something was different this time. At first, Melissa thought the pain was unfamiliar only because she hadn't felt it in a while.

But when I looked at my friend and saw that she wasn't wearing sunglasses, I knew something was different. Sunlight usually bothered Melissa when she had a headache. Without sounding an alarm. I checked to see if she had any weakness in her arms or legs and asked if she felt dizzy or out of it. I detected no weakness. She said she didn't feel dizzy but her neck bothered her and the headache was quickly becoming one of the worst she'd ever had.

I suggested we go to the emergency department. At the hospital, a CT scan revealed that Melissa's headache was due to a small subarachnoid hemorrhage (SAH), which is bleeding into the space around the brain. Nontraumatic subarachnoid hemorrhages are most often caused by a leaking or ruptured brain aneurysm or blood vessel malformation. Melissa had an aneurysm—a weakness in a blood vessel in her brain that had ballooned and filled with blood—and it had started to leak. Melissa was admitted to the hospital where the aneurysm was successfully treated.

Melissa was lucky. Her aneurysm was found before it ruptured. Less than a third of people who make it to the ED and get aneurysm surgery in time recover without any neurologic deficits. Sometimes aneurysms come with warning signs, but often, as in Melissa's case they are silent until they leak or rupture. The most common sign of an aneurysm leak or rupture is a headache. If you don't usually get headaches, then a bad headache warrants a trip to the ED. But if you already get migraines, here are some signs to look for:

1. The headache feels different from any previous headache.
2. You aren't experiencing typical symptoms such as light sensitivity.
3. The pain is more severe than anything you've experienced.
4. You feel numbness or weakness in the face, arms, or legs.
5. You have a stiff neck.
6. You are experiencing visual disturbances.
7. You have a past medical history of HIV, or autoimmune disease.
8. If you experience any of these, get yourself to the nearest emergency department.

Dr. Ganti is a board-certified emergency physician with fellowship training in vascular neurology. She is the mother of four boys and one girl and the author of more than a dozen medical textbooks. You can follow her on Twitter at @LathaGanti.