To be fully honest, being buried alive, or, being trapped in your body with no way to communicate is a nightmare of mine ever since both of my grandparents fell in a coma and never woke up again. So this was, in a way, working out my issues.

Your thoughts of Charon and Styx (which would almost have been the title, by the way) are rather appropriate, as murron and me talked about this on the phone when we plotted.
Lot's wife was another last-minute addition, but I'm very glad to hear it works for you.
Thank you for the detailed feedback - it's most highly appreciated.