Sleepiness after the third vaccination may be a normal phenomenon caused by insufficient sleep and emotional stress, or it may be caused by adverse drug reactions. 1. Lack of sleep: If the patient has stayed up late the day before the third vaccination, it will lead to the phenomenon of lack of sleep, which will lead to the phenomenon of sleepiness after the vaccination, which is a normal physiological phenomenon. 2. Emotional tension: If the patient has high mental tension before the third vaccination, it will lead to lack of oxygen in the brain, which will also lead to sleepiness after the vaccination, which is also normal. 3. Adverse drug reactions: when patients become drowsy after the third vaccination, it may also be caused by the adverse reaction of the vaccine. In addition to drowsiness, patients may also have symptoms such as pain at the vaccination site, and the symptoms will disappear after rest. When patients experience drowsiness after the third vaccination, it may be normal and does not require treatment. If the symptoms persist and do not disappear, medical examination is required.