Not sure what happened but the zero to 100 differences always amaze me. I can home from work and my wife and s12 were sitting at the table working in his merit badge stuff. No screaming and no tears. She was in a good mood and seemed happy. It is actually a bit scary when this happens, I know it's not going to last but because of how quick it went from bad to good, you know the trip back can be just as quick.
But I'm going to enjoy the cease fire as long as it lasts.
One of the things that I have learned is to work twice as hard on myself when things are calm and peaceful. That helps me to build up mental reserves so that when things do go south again I can do a better job of not getting reactive and defensive. Like waverider says, keeping your behavior consistent helps.