A seizure is an uncontrolled electrical disturbance in the brain caused by an abnormal electrical discharge. Reasons are head injury, stroke, or low blood sugar.
Encephalitis is a serious, potentially life-threatening condition that occurs when the brain becomes inflamed. It is most often caused by a virus, such as HSV.
Rheumatic fever is a serious inflammatory disease that can develop after a strep throat infection. It can cause damage to the heart, joints, skin, brain, etc.