Don't mind me thinking aloud...
So lyrium addiction is regular addiction (which is, of course, dangerous), made even worse by the very substance that one's addicted to, yes? It's being addicted to a literal poison-it will undoubtably eff you up, whereas one can drink some alcohol and not end up awful. Like, you don't have a legal lyrium drinking age or something, because even testing lyrium could have seriously lethal effects.
Fenris is undoubtably addicted, then, right? Or he would be, if he didn't have a constant supply of it? Or would that be even more torturous, because the thing he wants is right there, in his skin, but it's also causing him agony because it's poison injected into his skin, but then he'd feel better if he could have some lyrium, but-
*brain explodes*
Good job, Bioware. You broke my mind. I think Fenris didn't lose his memory because of the Magister/lyrium torture, I think you presented this quandry to him as a "the crowbar to open the box is within the box"/INCEPTION style problem.
In any case, I find lyrium very interesting, separate of it's place of origin. Ugh, caves. *shudders*