Seth isn't too worried until Daniel mentions Lucifer. Coupled with the mention of dreams 'bleeding over', that is in no way a comforting thought. He suddenly feels himself quite a lot tenser than a moment ago.

The news of what exactly Daniel had woken up with makes his insides grow cold. That is... messed up. Not that that is surprising considering who they're dealing with, but it's still pretty sickening. Seth has to make an effort to push aside his worries to actually deal with Daniel's question.

"Well, um... It's very unlikely to just happen, on its own," he answers, eyebrows drawing together. "But, er, there's people with powers like that, who can use the Dreaming to affect the waking world. And, hmm.. He has powers of manifestation, doesn't he? So he might be able to use that remotely... Lucy's apartment is warded though, so he shouldn't be able to get in there." Seth had figured it would be, but he had seen for himself when he came by to see Daniel, so.

The thought that Lucifer could do something like that to Daniel is... horrible, to say the least. The thought that he might actually be interested in doing so is even worse. Seth's plan for keeping safe has been to try to remain as unnoticeable as possible.