Haha we have the same experience. It was really challenging to balance our tendencies early in the relationship. She'd pack every hour of every day with activities and social events until I'd just get mean after extended periods without down time. It took her a while to understand that me enjoying having time alone was not a rejection of her or a lack of enjoyment in being with her. Just that I'm wired to be comfortable alone and need time to myself periodically. It's an almost unfathomable mind set though to someone like my wife or your sister. People are so interesting...