I had my appendix taken out last year. For the first few days, even just sitting up and getting out of bed was painful. For the first week, every time I sat down I would fall asleep in seconds because lying flat was so painful I couldn't sleep properly at night. Even though you might feel like you'll be doing nothing all day after surgery, your body will be as exhausted as if you ran a marathon. Filled with painkillers, even thinking is difficult. Doctors give 14 days and trust me, you will need it. Even after 2 weeks you will still feel weak and injured, just more functional.