Mack is unnerving sometimes. Sry about that, Mohinder. He's a nice guy, underneath the grump and occasionally creepy smiling. He smiles less creepily when he's genuinely in a good mood, at least? Which...is not now, unfortunately.
"No." It's a testament to how Mack's adapted to the nexus -- a man in his line of work has to be adaptable -- that he doesn't ask 'what superflu' or express much in the way of shock or confusion. "Details are classified, but the bullet mercifully quick."
Quicker than the seemingly slow and entirely sharp feeding process of the Wraith, which he became intimately familiar with. And yeah, he's sort of bluntly implying he did, in fact, die before he came here.