How do you make yourself miserable?

I've been reading Louisa Hay's book on healing yourself with positive thinking. It's certainly easier say than done. Right this morning, I meditated for an hour and felt just great. I was calm and energized and was thinking I should be able to start the day with very positive thinking. Tne next moment, my wife was calling our younger son to help with kitchen task and the boy responded in a very rude manner. I was very unhappy with his attitude and exchanged some harsh words with the boy. Then, as you can imagine, my "mindfulness" disappear in a snap. I've sensed it and I regret it immediately. Then what? I got stuck here. Do I work on my mind to regain the calm feeling or do I let go even the idea of getting it back and go on with my life today? Something not so settled here for a meditation practitioner. What would you do for now? What would you do in the future?