My answer is, "NEVER!" I never dread going to work and THAT'S worth something!
I've been excited about my career as a Realtor for the 7 1/2 years I've been in it. It's true, and I just realized this recently. I really can't believe it because, thinking back, I can remember days when going to work was a drag for whatever reasons. I get up in the morning with spirit and energy to get through my "to do" list and somehow, I always get through it.
I wish this of anyone, though life's not perfect and I realize sometimes life throws curve balls at us. I have to say, though, that my career in real estate even helps me get through those challenges. I can't say it's always easy, but I think anyone with young children and a career will agree that it's a juggling act, I'm just very skilled at juggling - now. Put me in this position right outside of college and I would have felt overwhelmed, and probable overmarried to responsibilities where now I thrive in these situations.
So if you wake up in the morning with a drabby feeling that you'd just rather stay home, I'd say pay attention to what it is you are trying to avoid that's wearing down on you. It feels great to not have that burden!