I would recommend Lords of Chaos first, as a primer: https://en.wikipedia.org/wiki/Lords_of_Chaos_(book)
Before digging into Until the Light Takes Us.
He have a special place in my personal music history. I started to listen to a bit extreme metal in the 90s and was a bit shocked by my own taste. From the early Metallica to death metal, it got steadily more extreme.
The limit was Darkthrone -- I got an album and (at least at the time) I felt physically sick if I used headphones! Years later, I saw that series of youtube interviews with Fenriz, discussing the music. He was so knowledgeable and, more or less, dismissed most genres I love in metal (Meshuggah, Nile, etc) as not really that interesting. :-)
These days, I can enjoy the early Darkthrone stuff, but it was a funny reality check to realize early that I'm not really that metal, I just like the music. :-)
The first album, for me, that gave me that physically sick feeling like you describe was Portal's Vexovoid record. We can debate whether or not Portal fits into the general category of Black Metal, but damn that album is just frightening.
Something about Portal reaches deep. It's odd because I'm not necessarily a huge fan of their music in terms of just listening to it as music, but I like how there's something exhaustively serene (in a twisted way) about the atmosphere, like a dark meditation/trance almost.
When I heard Portal before, I was more into a bit faster.
Portal's whole aesthetic plus the music really creates this inexplicable atmosphere, what I picture as if I had been tapped into the degrading mental state of Jack Torrance.
Deathspell Omega is a band that I can't get enough of. I remember listening to Si monvmentvm reqvires, circvmspice during an overnight drive from Halifax, NS to Sydney, NS and just experiencing moments of fear or sheer terror. Something that I can't say that any other album has done for me.
The new Deathspell Omega record is brilliant. IMHO they are at the forefront of current Black Metal.