[Coda]

Take an anger management course. What you describe sounds exactly like the same excuses I gave before I took one. You probably DON'T flip a switch as much as you think you do -- you just don't notice the buildup until the dam breaks. An anger management course (or at least, a good one) will teach you how to recognize the physiological signs of the buildup. It'll be more effective than just individual therapy with a general therapist.

For starters, your baseline cortisol levels are probably too high. You should be doing those breathing exercises for a total of half an hour a day ANYWAY even if you're not feeling angry or stressed out. Combining it with meditation is best, but even if you just have to do the breathing exercises while you're driving the car or something it's worth it. Fixing your cortisol levels will bring down your stress floor, so there's a larger range between "normal" and "angry."

I would also imagine you're not getting enough sleep. You should fix that. At least until your baseline stress levels go down, you need to make sleep a priority instead of sacrificing it for the sake of getting other things done.

Has your psychiatrist said anything about codependency? I don't know you well enough to know if it applies, but with that many children it's a possibility.