King was invited to speak at the Mason Temple church, but he still suffered from a migraine headache.

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Recently, the American Academy of Neurology and the American Headache Society released new guidelines for migraine-headache-treatment.

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Tension headaches can sometimes be difficult to distinguish from migraines, but unlike some forms of migraine, tension headache usually isn't associated with visual disturbances (blind spots or flashing lights), nausea, vomiting, abdominal pain, weakness or numbness on one side of the body, or slurred speech.

CNN: Tension headache

And one that quickly generated over 10 million views on YouTube, causing a migraine-worthy PR headache.

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It is estimated that more than a billion pounds is lost every year to the UK economy due to people taking time off work with severe headache or migraine.

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Migraine with aura is a severe headache preceded by symptoms such as seeing flashing lights, temporary visual loss, speech problems or numbness of the face.

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And, while physical activity typically aggravates migraine pain, it doesn't make tension headache pain worse.

CNN: Tension headache