Ah yes, the old hangover headache. It’s actually caused by a number of things. If you’re prone to other problems such as migraine, you could get more than you bargain for. But the hangover that most people are familiar with, after drinking too much the night before, is mostly a result of dehydration. Dr. Dan Small, a neurobiologist with the National Research Council in Canada, explains what this dehydration does to your brain: Dehydration makes it difficult for your body to produce cerebrospinal fluid (CSF), the clear watery fluid in which the brain floats. There is about 150ml of CSF in your body, but it is replaced at a very high rate, about four times a day. When you are dehydrated by alcohol, you produce less CSF and there is less fluid in your cranium to cushion the brain. Your hangover/headache after your evening of overindulgence is actually a signal that your CSF levels are low and your brain is banging around inside your skull.
So what can help? Drink some water before you go to bed to help counteract the diuretic effect of the alcohol. (Or, better yet, drink water in the first place!)
A medical procedure actually causes the same problem – a lumbar puncture. The purpose of a puncture is to take out CSF, usually to test for things like meningitis or encephalitis.