Headaches

Headaches are a common side effect of spiritual experience.  They are also frequently experienced  by those with an inherited ability to have spiritual experience.

Although the headaches are often very severe this would not be classified medically as migraine, which has a different medical explanation.

Many people who experience out of body sensations suffer from truly severe headaches. 

One of the characteristic experiences, where the input is being received in the form of a dream,  is to wake about three or four in the morning with a headache of unbelievable severity.  The headaches of this kind are not localised, but seem to be inside the head fairly centrally placed [I talk from experience here].  They can make you violently sick and virtually incapable of walking or seeing. 

In the spring of 1811, for example, Beethoven became seriously ill, suffering headaches. On the advice of his doctor, he spent six weeks in the Bohemian spa town of Teplitz. The following winter, which was dominated by work on the Seventh symphony [a manic phase], he was again ill, and decided to spend the summer of 1812 at Teplitz.

There is no single physical cause.  Obtaining spiritual experiences of this level puts great stress on the mechanism of the brain – like overloading the computer with too much current.