>but rather the other additional circumstances of the "solitary jail life" which are mitigated for "ordinary prisoners".

In my own comment, I wasn't clear enough that I also had this in mind. There's a lot you can do to make your own environment comfortable. In prison solitary, nothing at all.

Coincidentally, I just finished reading this book. It gives an incredible view into the mind of a hostage kept in similar conditions: https://www.amazon.com/Hostage-Guy-Delisle/dp/1770462791/

(On the off chance you read French, it's originally in that language, and probably better to read that way if you can)

I picked it up for bedtime reading and couldn't put it down. I read the entire thing, into the middle of the night.