Definitions of slump:

• noun:   a noticeable deterioration in performance or quality

  Example: "The team went into a slump"

• noun:   a long-term economic state characterized by unemployment and low prices and low levels of trade and investment
• verb:   fall heavily or suddenly; decline markedly
• verb:   fall or sink heavily

  Example: "He slumped onto the couch"

• verb:   assume a drooping posture or carriage
• verb:   go down in value

  Example: "Prices slumped"