Cluster Headaches: Symptoms
Cluster headaches are distinct from migraine and tension-type headaches. These "alarm clock" headaches may strike in the middle of the night, and often occur at about the same time each day during the course of a cluster. Cluster headaches usually occur repeatedly on one side of the head and cause intense pain that feels like a stabbing sensation in the eye. Additional symptoms may include:

• Excessive tearing and redness of the eye on the side of the head affected by the pain
• Nasal congestion on the affected side of the face.
• Red, flushed face.
• Reduced pupil size.
• Drooping eyelid.

Triggers
During active periods, factors that may trigger attacks include:

• Alcohol
• High altitude
• Air travel
• Bright sunlight
• Exertion
• Foods high in nitrites
• Drugs that dilate the blood vessels (including nitroglycerine and various blood pressure medications)

When the cluster cycle is inactive, these triggers usually have no effect.