We all get headaches from time to time. They can be brought on by annoying but manageable reasons such as stress, dehydration or your menstrual cycle, or they could be the result of an ongoing medical issue, such as migraines.

But how can you tell when a headache is a symptom of an even more serious or life-threatening problem? Here are some signs to look for.

1. You have speech or vision changes

When a headache is more than just a simple headache, you will also have other symptoms. If you also have changes in your vision, trouble speaking or walking, or weakness on one side of body, you could be having a stroke.

A stroke occurs when the blood supply to your brain is cut off or severely reduced, causing cells to die almost immediately. Migraines with “aura” can be confused with a stroke, but they often give you added sensations, such as tingling in the body or flashes in your vision, whereas a stroke takes away sensations and results in a loss of vision or lack of feeling in the hands.

Even if you get migraines, the pain you feel from a headache during a stroke will be different – for example, a headache that comes on very suddenly is likely not a migraine and could be caused by a stroke. But it can be hard to tell the difference, so if you even suspect you may be having a stroke, call 911.