Comment by phainopepla2

If you're regularly waking around 3 (as opposed to random times throughout the night) you might want to reconsider cortisol as a possibility, at least as setting a baseline wakefulness that allows you to be easily woken up from a noise. There is a natural cortisol spike at that time, and that combined with elevated levels from background stress causes the same problem for many people who fall asleep without issues, myself included.