Maybe the gagging problem is connected? It was just a thought. I'm sorry you're still getting no answers. That's hard. Maybe if you had a sleep study then they might pick up on something that's waking you up at night.
You can't go on without sleep. In the meantime try some of the remedies. I've never used Melatonin myself but some find it helpful. Inositol makes me less anxious but it doesn't help me sleep as such. I do use Tryptophan from time to time but not that often. Only when really needed. It knocks me out really well. I also get restless legs at night, and have done all my life, so extra magnesium helps with that.

Unfortunately it's all trial and error a lot of the time. Check out bluesfan's post too about the blood sugar levels and cortisol.

p.s. You don't have gastic reflux do you??