"You can do this."
That's what I tell myself, anyway. I've had a couple of really stressful times in my life, and I look at what I've learned, and you know what? After all that, whatever comes next is pie.
Stop, and Just Breathe. It's amazing how often we forget to take just a couple of deep breaths.
Don't focus on anything except what's in front of you. Sometimes, you just need to look at right now. It's like having a newborn, those first couple of months. You don't think about all the things you have to do, you just get up and do them, as needed. Sure, some of the less important stuff didn't get done, but life happens.
Do something physical to force the tension out of your body. Punching a heavy bag is good. Jog/walk/jog - it takes me about 2 1/2 miles to really feel a relief in the tension. Scrub something. DH knows I'm stressed, by how clean the house is.
I've learned, too, that I am much better at handling stress than DH is, and I can affect his levels a lot. There are some days when he really needs to be needed, and there are some days when he really needs me to be self-sufficient. I'm still working out the finer points of that, but it's there. (Can I share a secret? I have a stool, and a pair of rubber-tipped kitchen tongs, but if DH is home, well, he's taller than I am, and it's super helpful if he could just reach that down for me.... The trick is knowing when to have great balance, and when to need help with high shelves...)
Eating Ben & Jerry's out of the carton (or raw cookie dough!) while snuggled on the couch together and watching one of our "guilty pleasure" TV shows helps, too. (So does telling him, when he's on the way home and calls to see if I need anything, that he should pick up said Ben & Jerry's!)
Being generally silly. Like making up bad lyrics to songs. I know he's zonked when he makes up a bedtime song for our five year old from old commercial jingles. Or silly daydreams, or whatever. Relax the brain a bit.
Hang in there, lady. You'll be okay.