Headaches at 4.00am sound like they might be blood pressure related... More heart attacks happen at 3-4.00am than at any other time apparently.... the body is at its most relaxed and deepest sleep part of the pattern. Maybe your headaches are just your brains' way of telling you to keep the old pump going.

Whilst in hospital suffering with chest pains, I was awakened from a deep sleep by a nurse standing over me with adrenalin shot in hand, and monitors bleeping rude messages in morse code... my heart rate dropped below 35 and my pressure crashed... it was 3.54am.

Headaches usually fall into two categories. One where the blood vessels to the brain are constricted and so blood can't flow properly - fixed with a caffeine or sugar shot and the other is the opposite - blood vessels expanded (dilated?) usually by caffeine or sugar and so too much blood is allowed in. At 4.00am, if you're asleep, it's probably the former problem.

LTS