Don’t you have sore throat in the morning?
If so, that is caused by dryness. If throat or pharynx becomes dry, mucus protecting those area disappears. As a result, throat becomes sore. There is also a case that it is a sign of the beginning of a cold.
Common sore throat in the morning is caused mainly by dryness. It is alleviated by moisturizing throat taking water.
Sore throat caused by acid reflux (reflux esophagitis)
If sore throat continues without dryness, it can be caused by acid reflux.
There is stomach acid in stomach which dissolves foods. Stomach acid should stay in stomach. After eating, stomach acid increases. If you sleep right after eating, stomach fluid flows back to throat causing sore throat.
There is esophageal hiatal which prevents the backflow by tightening up of diaphragm, but with age or relaxation by drinking alcohol, it becomes loose. (Fig. 1)
Why does acid reflux cause sore throat in the morning?
Lying down makes stomach acid easily go up to throat.
For about 2 hours after eating, stomach acid is secreted to digest foods so the backflow of stomach acid easily happens. In such condition, if lying down, the level of stomach and throat becomes almost the same so stomach acid easily goes up to throat. As a result, the strong acid hurts throat.
To prevent acid reflux, it is better to go to bed at least 2 hours after eating.