Wow, this is a very well done sort of creepy. I like it.
However, I'm worried about balance for Insane Clarity. How long do those extra spell slots last? And could, say, two 4th level spells be used to make a 5th-level spell slot, which, when combined with another 5th-level spell slot, could create a 6th-level slot? If so, a Sor10/Anath10 could concievably have one 1st level, one 3rd, 4th, 5th, 6th, and 7th-level, and eight 9th-level spell slot, a bit much. Eight reality maelstroms can really ruin someone's universe (or day).
Or, starting with fifth level spells and sacrificing upward, the same character could have six 0th, 1st, 2nd, 3rd, and 4th-level slots, one 6th-level slot, TEN 8th level slots, and three 9th-level slots.
These don't even factor in any bonus spell slots for a high Charisma modifier. Maybe a use/day mechanism could prevent that kind of literally insane modification.
Also, what's with the (relatively) large number of water themed spells in the additional spells list? Did I miss something in the fluff that explained that?
The six additional 5th and 8th-level spells known are a bit much, maybe five should be the maximum number of extra spells known for any given level gain? The Anathema Mage is still going to be able to gain spells known besides that list, after all, and there was a balance reason behind letting a sorceror have only three 6th through 9th-level spells known.