Definitions of sinking:

• noun:   a slow fall or decline (as for lack of strength)

  Example: "After several hours of sinking an unexpected rally rescued the market"

• noun:   a descent as through liquid (especially through water)

  Example: "They still talk about the sinking of the Titanic"

• noun:   a feeling caused by uneasiness or apprehension

  Example: "With a sinking heart"