What causes tongue inflammation on the sides?

More questions:: Does it hurt? How bad is it, and how long has it been that way? The tongue could swell for a number of reasons including but not limited to injury to the tongue (biting or external injury), a local reaction to an irritant in your mouth, or an allergic (system-wide reaction). Determine which of these it could be (if any and consult with an oral surgeon, ENT or your pcp).

Tongue chewing: You may be chewing on your tongue. Thus can happen during sleep.

Biting: In many cases, tongue inflammation on the sides only is caused by biting on the tongue. To rule out any issues, it should be checked by your dentist.