Encephalitis is an inflammation of the brain. The usual cause is a viral infection, but bacteria can also cause it. Cases can range from mild to severe. For mild cases, you could have flu-like symptoms. Serious cases can cause Severe headache Sudden fever Drowsiness Vomiting Confusion Seizures For mild cases, you may just need rest, plenty of fluids and a pain reliever. For severe cases, you might need to be hospitalized. Fortunately, encephalitis is uncommon in the United States.