I was just coming on here to ask about this same problem... I've been using Fitday for about 3 months and it never occurred to me I would need to log the time I'm asleep!
I walk at least 10 miles a week to and from work, when I'm at work I'm standing or walking around for at least 20 hours a week, and some of the time involves heavy lifting or carrying, add to that the mountains of grocery shopping I carry home on foot every week - but for some reason I didn't feel comfortable selecting even 'mostly seated/some movement' as I felt the calories it allowed me were too high, so I've been choosing 'seated all day' but felt that was just a smidge low plus clearly I'm NOT seated all day. Now I know why! Fitday could do with adjusting their calculations a bit better if we're all having the same kind of problem, it seems silly to have to log sleep when you're not meant to, or have to choose the wrong activity level.