Would putting a baby monitor in his room for a while work? Or maybe you could give him some kind of noisemaker or phone to reassure him that he could get help if he needed it.
When I was a teenager I got into mysteries, and after binging on Agatha Christie, phyllis Whitney, etc. I ended freaking myself out. What helped me was a) changing my reading material and b) Psalm 27:1 (I realize that it may not be helpful to everyone, but as a Christian it was very comforting both then and at other times I was fearful. If your family has any religious faith, you might find something in it to comfort your son and calm his fears.)
Psalm 27 King James Version (KJV)
27 The Lord is my light and my salvation; whom shall I fear? the Lord is the strength of my life; of whom shall I be afraid?
https://www.biblegateway.com/passage/?search=Psalm+27&version=KJV