Nameless Dread

AKA "vague, nameless dread."  With a few minutes' googling it seems to come from A. Conan Doyle's A Study in Scarlet... but it sounds more like Poe.  (Through the miracle of the Search function it looks like Watson, in the same book, compares Holmes to a Poe character, and Holmes dismisses it.)  Sic transit dark 19th-century stuff - their version, I guess of noir.

What this is talking about, anyway, is the emotion of fear without knowing its cause.  In the middle of the night, not so surprising, could have come from a dream you don't remember.

But at high noon it's unwelcome.  Beat it.