My sleep-onset difficulties are not as severe as yours. I nevertheless rely on a relatively strict "bedtime ritual" to prime my mind for sleep.

1. I slowly and fully back out of my computer and power down.

2. I take my nighttime meds including an antidepressant and an antianxiety med.

3. The room cannot be totally quiet. If it is too quiet, I start to ruminate and that can lead me down the wrong path. I set the TV timer and select a program that is neither too interesting nor too boring -- the goal is to take my mind off the process of falling asleep without stimulating me; a form of light distraction. (Yes, I know that the official canons of good sleep hygiene frown on having a TV in your bedroom. This technique, however, is the product of years of trial and error.)

4. Being slightly too cold doesn't prevent me from falling asleep, but being too warm will.