ON THE RUN DE-STRESSING EXERCISE:
If you're busy, on the run, or just too activated to settle enough to do a longer breathing exercise, this one takes very little time, and can even be done while doing stuff. It's called the 'Physiological Sigh'. Here's a short 3-min video that explains and demonstrates it.
https://www.youtube.com/watch?v=vTCA3VDgeDs