The thing about a cave nap has me thinking they might have dust mite poop allergy. You virtually cannot escape dust mites in a regular human home. And a major part of the dust in our homes is dead skin cells, which dust mites feast on and then they poop a lot.
If you always sleep in a bed permeated with skin cells and poop, and you're allergic to that, then not sleeping in that for a change will be the first time in an eternity where you get some actual rest...