Hello, I can understand your concern for your mother s health. Lethargy and tiredness after surgery is not common. Some common causes are prolong bed-ridden condition, old age, inadequate diet, dehydration, anesthetic medications. If she is lethargic all the day with lack of interest in any activity, this require prompt action with finding the cause for it. She must be encouraged to walk for some time. She must have regular food intake. Surgery at old age, inadequate food intake due to fear of pain might be responsible for lethargy in your mother s case. (Otherwise appendectomy itself is simple procedure) Hope I answered your query. If you have any further query, I would be happy to help you. Have a good day!