When I read Pretzel's comment I actually pictured Debra getting knocked on the head and developing amnesia. That's the level to which this show has sunk, that I could honestly picture that.
That said...that scene plays out pretty well for me. (Spoilers? Do I even need to say this?) I'll have to see where it goes from there, but of course Dexter wasn't going to just come clean, and it's just as obvious Deb is freaked out. If she accepts his explanation and never thinks about it again that will be staggeringly lame, but I think this is her Skylar White moment, where Dexter starts to ease her into what he does by playing up his feelings about Rita.
Of course, this show isn't fit to lick Breaking Bad's asshole, but they can watch and learn, surely?