I think identifying and defining the stress specifically helps. When I have a big meeting or something on the line, I feel a sense of performance anxiety, kind of like sitting in the locker room before a big football game starts. It's not the idea that I have to perform per se, but maybe potential weak links in my performance can worry me and keep me up.
What helps me is a mental "pep talk". A coach in my analogy will give a talk, build confidence in his team, remind them of all their practice and preparation and when you hit the field the butterflies turn to energy.
Anyways, I find it helpful to remind myself of how prepared I am, how ready I am, how my event will be a walk in the park.
It helps me to be organized, rehearsed, prepared....ready, what ever that means for you, beyond a doubt. And, if I'm not totally ready, I fix what ever is unprepared until I'm comfortable with it. Then, the activity is my cakewalk to make and it's waiting for me, not the other way around.
Also, ambien. Or nyquil. No doubt unhealthy for regular use but for random sleepless nights they are each certainly helpful and stronger than melatonin by a long shot.