So suspicious. I wonder what reason I've ever given you for it...

[Just lying about everything since I popped into existence. He has the upper hand here, though, and knows it. Chained to his unconscious counterpart, he has all the power over this situation, effectively holding the real L hostage.]

Don't worry. I'm sure I'll find some way to entertain myself. His heart rate's faster than it was an hour ago, so he'll probably wake up pretty soon. Won't that be fun?

[Sarcasm in spades, there, but it's a little subtler than this doppelganger's really prone to demonstrating.]