This doesn't tell us anything, and drinking water alone isn't enough. How much and how often did you drink water, and consume salt or rehydration salts. The lat

This doesn't tell us anything, and drinking water alone isn't enough. How much and how often did you drink water, and consume salt or rehydration salts. The latter is just as important as the former in keeping your body functioning. If you experience significant salt loss, you will get a headache as your body tries to maintain homeostasis. This is exactly one of the reasons for the headache part of a hangover, and if you adequately replenish your water and electrolytes, you will be vastly less likely to get one.