Final answer:
The priority action by the nurse is to check the client's blood glucose level to determine if it is low.
Step-by-step explanation:
The priority action by the nurse is to check the client's blood glucose level. The symptoms reported by the client are indicative of hypoglycemia, which occurs when blood glucose levels are too low. By checking the client's blood glucose level, the nurse can determine if it is indeed low and take appropriate actions to address the situation.