I woke up with a 2 red sores in the back of my left side tongue. i have not been sexually active , it went away in a day. what was it ?

Stomatitis: It sounds like stomatitis, an inflammation of the tongue. It can often appear for no particular reason. If it does, gargling or over-the-counter treatments can help with discomfort. If it persists, check with your doctor.

Bite marks, virus?: The two sores that you had in the side of your tongue could be anything. But since they disappeared so quickly, they might have been a minor virus or more likely you bit your tongue (grinding?) while you where sleeping.