A single person in an air-tight average sized room could survive on the available oxygen for about a week. So I suppose if you're in a perfectly air-tight room

A single person in an air-tight average sized room could survive on the available oxygen for about a week. So I suppose if you're in a perfectly air-tight room and no one comes and goes at all or opens a window, you could die eventually. Even if you're relatively reclusive, assuming you go outside once a day to get the mail... you'll be fine.