the pit of (one's) stomach
An area in the core of one's abdomen, approximately in or near one's stomach, in which one feels a physical response to strong emotion, especially fear, stress, or anxiety. I've had this awful feeling in the pit of my stomach all morning because I know we'll be finding out the results to the final exam this afternoon.
pit of one's stomach
Fig. the middle of one's stomach; the location of a "visceral response." I got a strange feeling in the pit of my stomach when they told me the bad news.
the pit of your (or the) stomach
an ill-defined region of the lower abdomen seen as the seat of strong feelings, especially anxiety.