After a head injury, which usually develops right then and there, there are certain symptoms of headache, dizziness, nausea and vomiting. In severe cases, numbness and weakness of the limbs and speech dysfunction may occur. But there are also people, such as the elderly, who do not show obvious clinical symptoms after a head injury. At a later stage, a delayed subdural effusion, or a subdural hematoma, etc., may develop. But this usually lasts for 1-3 months, and then there is nothing too specific, unless there is a very, very specific case where epilepsy occurs. This tends to occur within 1-2 years after the injury, in other cases it is particularly rare, basically negligible, so for head injuries, the onset of the disease at that time and the maximum length of time not more than 3 years.