Your symptoms sound similar to me. Back in the 80's, I took a fall down a flight of stairs, I started head first and somehow ended up landing back wards, meaning I hit the back of my head, wow, it hurt and sure scared me. Well, for a couple of days, I was fine, then all of sudden one night as I was getting ready to sleep, I had a massive adrenalin rush and felt like I was dying. I jumped out of bed and sat in a chair in the living room, I was petrified and all alone.