sinking feeling, a
A sense of dread or apprehension, as in I had a sinking feeling that I'd forgotten my ticket. This expression employs sink in the sense of “become depressed,” a usage dating from the early 1600s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.