(Image credit: Getty Images) I went through a period of waking up at 3 a.m . most nights and it felt nearly impossible to fall asleep again. I tried everything from breath techniques designed to calm my nervous system, to getting out of bed and 'pottering' in another room, but nothing worked. After repeated 3 a.m. wake-ups that were draining me of energy the next day, I decided to get to the bottom of not only why I was waking up at 3.a.m, but how to fall asleep fast again in the middle of the night. Key take-aways: At a glance The 3 a.m. wake-up fix: Cognitive shuffling is a mental exercise designed by cognitive scientist Dr. Luc P. Beaudoin to stop racing or busy thoughts that keep you awake at night. The 'brain-flip': Cognitive shuffling flips your brain into a 'pre-sleep' state by mimicking the random imagery we experience right before drifting off, and is a science-backed way to fall asleep fast again if you wake up at 3 a.m.…