Hi Dima.
1. For me, stress has always been huge trigger (finals, 30 years ago, in college; birth of kids; job transitions; etc.).
2. Most folks do get hit most often at night I find that, early in a cycle, there's not much pattern; but over time the evening becomes a ritual (up at 11; 12:30; 2; 3:30;5;give up and make coffee).
3. I can't overstate how important oxygen is. I tried it multiple times over many cycles (and multiple years) before I figured out how to do it successfully. Search the forum and find the right regulator (15 lpm minimum), non-rebreather mask, and