I'm going to assume this has something to do with god items.
Fact #1: Deep sleep doesn't prevent the server from letting you talk to NPCs.
This is important. But then...
Fact #2: Deep sleep appears to prevent the client from initiating an NPC dialogue.
So it would seem that you can't legitly talk to NPCs while in deep sleep, right?
Well... not quite. Deep sleep doesn't
directly prevent you from clicking on NPCs. It just "freezes" your character (much like what happens when your cast is interrupted by spell breaker), and it is this freezing, not the deep sleep, that blocks the client. Anything that breaks the freeze, such as getting hit, or moving, will let you talk to NPCs again even if you're still in deep sleep.
There's another event that breaks the freeze, which I didn't mention above because I'm saving it for emphasis:
resurrection. That's right: the moment you self res or get ressed, your character is no longer frozen on the client side and you can click on NPCs to your heart's content. Conclusion: DSL is useless against dead characters trying for god items.