Why do we get headaches?

There is a range of different types of headaches, from the dull ache of a tension headache to the migraines and cluster headaches that are called "vascular headaches". Tension, or stress headaches are caused by tightened muscles in the back of the neck and scalp. The tension can be caused by a variety of things, from anxiety to eye strain caused by bad glasses.
On the other hand, vascular headaches occur because of changed blood flow to your brain. Scientists don't quite know why: for instance, it could be due to a localised lack of oxygen caused by a spasm in the cerebral arteries; or caused by blood vessel swelling. We do know that migraines can be triggered by the weather, by diet, bad sleep or stress. They tend to last between 4-72 hours, and some people report bright flashes of light or other visual disturbances.
We still don't know what causes cluster headaches, which can last for weeks or months, but scientists think that may be related to blood flow to the brain.
Read more on: http://www.bbc.com/future/story/20140214-why-do-we-get-headaches