disappointment

• A false dawn

  A situation that initially appears to be a positive development or improvement, but quickly turns out to be misleading or temporary.

• A sour note

  An unpleasant or regrettable aspect that spoils an otherwise positive situation or event.

• To come down to earth with a bump

  To face reality and the difficulties of a situation after a period of unrealistic optimism or fantasy, often with a sudden and harsh realization.