If the patient has vague pain in the upper left side of the head, it is mainly due to the following aspects: 1. migraine: ask the patient if he has any previous history of migraine or any history of headache attacks in his family, and consider the possibility of migraine if he has vague pain in the upper left side of the head. 2. muscle tension and vascular spasm in the brain: ask the patient if he has no nausea or vomiting, how he usually sleeps, and if he has fever when he has vague pain. 3. Intracranial aneurysm: If the pain is chronic for a long period of time, a vascular examination of the brain should be performed to find out if there is any intracranial aneurysm, as some patients have intracranial aneurysm, which can cause vague pain in the upper left side of the head.