There are several reasons why patients feel pain in the left back of the head after drinking alcohol: firstly, it is considered to be related to the nerve stimulation of the patient’s brain by the ingredients in alcohol. The second aspect is considered to be caused by the vasodilation of the patient’s blood vessels when drinking alcohol, which can cause the stimulation of pain-sensitive structures in the patient’s brain, such as the posterior occipital region, which is rich in capillaries and prone to pain in the back of the head area. Third aspect. If the pain is very severe in the left side of the back of the head after the patient drinks alcohol, it should also be considered that it is caused by an increase in blood pressure caused by alcohol consumption, resulting in bleeding in the left cerebellum. If the patient is accompanied by unstable walking and body slanting to the left, he or she must promptly visit the hospital for examination and treatment.