Meditation/breathing exercises (you must PRACTICE these)
Don't sleep on this one; when I first moved back to Connecticut it was with the specific intent to get divorced (long story) and the first six months or year was a REALLY stressful time for me. I even ended up in the hospital for about four days - the first and only time I've ever been admitted (so far). It was a condition that I still technically have, but I've not had a recurrence in nine years (fingers crossed). One of the things that my doctor said to try - and even he said "now, don't laugh at me, give this a try" - was a series of breathing exercises. I did them a couple times a day and while I don't do them much anymore, there is still the odd occasion where I will. It just seems, for me anyway, to deescalate everything my body and brain is going through in that moment. It's like a way of regulating, of turning the thermostat.