Cluster headaches are the most severe kind of headaches. They’re often described as excruciatingly painful. This type of headache often wakes sufferers up from a deep sleep because it’s so painful. Cluster headaches occur daily for long periods (weeks to months) and then stop for some time. But, they may return when you least expect it. The cause of cluster headaches isn’t certain, but it may be connected to irregularities in the body’s biological clock (hypothalamus). Cluster headaches usually don’t have triggers, but alcohol can make them worse.