Pregnancy and Exertion?

So why is it exactly that people always coddle pregnant women? Is it because there is actually something that can happen from "overdoing" it?

Today I definitely overdid it. I feel like shit. I called my friend to come over because I felt like I might faint. I'm lightheaded and shaky, of course that could be sugar/Halloween related, but I don't know. Also, I am clearly not getting enough sleep.

Today I did some dyeing, sewing, cleaning...took the kids out for breakfast, took Laszlo to school...went to the hardware store to pick out paint colors...went into the garage to attempt putting things away after 2 weeks of construction (not in that order). I think between the up and down on the step ladder and cleaning the dust off the boxes I was putting away, I just did too much physical stuff. I always believed that if you weren't at risk for preterm labor, that you could still do everything you'd normally do...even at 7 months pregnant.

Am I wrong about that? Please someone in the know, clarify.