You didn't answer the question. The person clearly told you that they had a drink of water in the middle of the night and got a headache. They did not eat. Read it again and answer it properly....Doctor!
Hi,
Dehydration is a common cause of headache. But there are not enough studies proving that drinking water can lead to the development of a headache. Water is very important for the proper functioning of the body. Headaches may be triggered by a lot of factors including the food you eat. Try to have a headache journal and write everything that you eat and do to determine the possible trigger. I suggest that you continue drinking water or fluids to avoid dehydration. If it persists, you may need to have this evaluated further for proper management. Take care and regards.