The metallic taste and speech issue, the incredible head pain, sounds more like Bells Palsy.

I had Bells Palsy in 1999 and I experienced the same symptoms.

I lost my taste buds to the metallic taste. I had the really bad head, neck and shoulder pain. I had speech problems; could not pronounce words that started with "S" and certain other letters. Since Bells Palsey was on the left side of my face, my left eye stopped blinking.

I hadn't thought about it, but since you posted about your symptoms, I am now wondering if Bells Palsy may have brought on the burning smell for me.