Thirsty before bedtime, there may be the following reasons: 1, did not drink enough water before bedtime, water is the source of all life activities, various physiological activities in the human body need the participation of water. So if the amount of drinking water is not enough, it will affect the physiological function, it will lead to insufficient blood volume, the amount of saliva secreted by the salivary glands is reduced, the oral mucosa will feel dry and also feel thirsty. 2, it is possible that the dinner ate too salty food, if the dinner ate a lot of very salty or very greasy food, it needs a lot of amount of water to participate in the digestion of food, so that is will feel thirsty. In addition, eat too salty food, in order to dilute the sodium ion, also need a lot of fluid or saliva. Excessive sodium ions in body fluids will also cause a lot of water to be absorbed into the blood vessels, and you will feel thirsty.