Concussion is a relatively mild form of traumatic brain injury. The main clinical manifestations are disturbances of consciousness, usually including disturbances such as unconsciousness, but typically not exceeding half an hour. There is also recent memory loss, and the inability to recall the incident causing the injury. Some patients may experience dizziness, headache, nausea, loss of appetite, insomnia, tinnitus, or difficulty concentrating and decreased memory. Additionally, a very small number of concussion patients might experience a low-grade fever.