Hi @hipcheck, every bottle of melatonin comes with a warning not to use it it if you have an autoimmune disorder. Have you been screened for one? Your symptoms sound similar to ones I had with Polymyalgia Rheumaticia.
Generally, if you have PMR, your inflammatory markers, from blood tests (ESR and CRP) will be elevated, although if your symptoms are relatively new, they may be normal, or only slightly elevated for a while. PMR and its sister disorder Giant Cell Arteritis (GCA) are treated with Prednisone, which makes sleeping difficult. I found lemon balm tea to be helpful. (There is a PMR and GCA forum here on Connect).
When I had the gagging symptoms, I thought they were vagus nerve related so did exercises for the vagus nerve. (These can be Googled) Those symptoms eventually went away, but they were hell when I had them, over a period of nine months. Sometimes the retching would wear me out for the day. I also lost about 17 pounds, being unable/reluctant to eat, fearing the gagging attacks.
I stopped using melatonin when I was diagnosed with PMR and GCA, but to be honest, it never really improved the quality of my sleep. I've been reading lately that it may have a positive effect on bone density so I considered taking it and consulted my rheumatologist, who wasn't aware of the autoimmune connection! He told me that many of his patients with autoimmune diseases take it. Now I'm more confused than ever, but I think I'll avoid it for now.
My husband has Alzheimer's Disease and his neurologist suggested I give him Melatonin at night to settle him down. It stops him from talking in his sleep. So far, so good.
I wish you the best and hope you get to the bottom of this.