> I've been trying to track my triggers and things. And yesterday otherwise was completely stressful. So I have no idea what caused me to switch on and be able to focus like that.

Maybe having a stressor that you could safely block out gave you the pressurization to do something else with focus. My best music practise was always when I knew there was a deadline like having to leave to go out or having the house to myself until people came home, and then I could concentrate fully knowing there was an end to it. In your case, knowing you could safely set the stressors aside and be free from them by being absorbed may have been the draw. Just an idea - of course I have no idea what went on in your mind.