Stop doing the extra hours. You've already said the targets are not achievable so don't bother working extra hours as you wont be reaching them regardless of the amount of hours you do.

You need to be careful with taking stress leave in the work place. In my experience most people who go on it never return to the company.

I was under a lot of stress during my pregnancy & I did some research & found that everyday types of stress including work stress are not dangerous to your baby. The kind of stress that is dangerous is the loss of a partner (death) or a traumatic experience of some kind like a car accident or being attacked etc.

Try to not stress, but I know that's hard. Once you've had your bub your job just wont matter like it does now. By the way, your brain does not always go back to "normal" after giving birth. My brain is almost as befuddled as it was when I was pregnant & I find my job harder than I did before being pregnant. My mind is just on other things now.