There might be physical reasons behind burnouts. A personal example -- a simple bacteria infection in a tooth, which didn't give any normal problems like pain

There might be physical reasons behind burnouts. A personal example -- a simple bacteria infection in a tooth, which didn't give any normal problems like pain etc. Allergies can make you tired -- and some (well, at least mine) food allergies won't have much throat effects, which makes them hard to identify yourself. So check up on physical health, too.