A friend of mine, female, 20 years old, living kind of a stressed life, wakes up at 7:00 AM had some breating problems in the last few weeks.
In that time she noticed that the pain gets really really more between 12:00 AM and 3:00 AM, sometimes she would be asleep in that time, sometimes not.
So why do u think this happens ? (if you need more info, please feel free to ask).
My explaination is that she would get extremly stressed at that time (after a long day).