Usually what happens with an overstressed Mom is that she just stops making milk! The baby gets less milk when nursing, and THAT makes for a cranky baby. The absolute BEST thing is enough rest. Nap when the baby naps, if at all possible, is the best advice. That's fine with the first one, but each subsequent bambino makes that suggestion harder to follow without some help around the house.
I was careful to never sleep with my jedis when I was exhausted and I never took any medications while breastfeeding. Even while "asleep" I was constanly aware of their presence, and it remains even to this day, although not as strong.
Nightime nursing while asleep was the absolute best for both of us...once I figured that out, Matthew slept and nursed on and off all night, and Joshua slept throughout the night from the very first. We both woke up rested and content in the morning and ready for fun.