PA as IC says, you are pregnant and allowed to feel tired, and if you end up being at home while your DH works, then you will find a way.
To be honest, the leap from one to two LOs is nothing compared to the adjustment you have to make from zero to one. When DD1 was born, it felt like chaos for the first few weeks, then we settled down into a way of being (reluctant to use the word "routine") that suited us. I was dreadig that same feeling with DD2, but the chaos just didn't happen. I suppose we were more confident (though I had had a lot to do with my sister's children, so I wasn't naive about babies), but also we already had a routine set by DD1, so DD2 naturally fell into it. Not that we enforced it, but she started wanting to go to bed at 7:30pm within two weeks of being born, and I'm sure it was because DD1 was going to bed. Similarly, she would often have a nap at 5pm or so, because she would be in the carrier or pushchair when I went to collect DD1 from nursery.
Honestly, two is fine!
As for going from career woman to SAHM, you'd be surprised how you can get your head round it. I never thought that I'd want to be a SAHM, but now I see how little I actually earn after taking out everything else, and think about school holidays and wraparound care etc, I just don't know that I can balance it with working, and I would rather be a SAHM than rush around all the time, and have my children shuttling between different childcare settings. I have friends who do it, and I admire them for making it work, but it looks ever so hard, and I can see the toll it takes on both them and their LOs. Equally, I can see that the lot of a SAHM is not all lovely baking and coffee mornings, but then as I've said before... Mums can't have it all!
Gone on too long. I'll disappear now.