Seriously, there's nothing more terrifying/horrible to me than insanity or senility. The idea of losing yourself is just horrifying.
And for Severus to lose himself in a such a way. No, he doesn't go to happy crazy land where he and Lily are together with a dozen babies.
(Of course not, it's you we're talking about)
No, you had to go...well, exactly where I thought you'd go. You tear my heart up, darling, you really do. And the device to restrain...you used it perfectly.
This was beautiful and terrible and a testament to your writing skills.