I was an emotional wreck throughout both pregnancies, and for the first year of ds1's life.
Ds1 is as well balanced as a bloody gyroscope. His two year old tantrums used to last seconds. Yes, they do pick up on atmosphere, but personally, I doubt they care. Ds1 certainly didn't.
Babies tell you when they are unhappy, they scream continually, until you do something to change that state of being for them. They are not subtle creatures!