Related Clues:

• Unhappy about rising soufflé ingredient – sank in the middle!
• Hung down loosely
• Artist returning without painting finally dropped
• Ran out of bravado
• Wasn't stiff
• Had unwanted flexibility
• Showed age, like a sofa
• Took a dip?
• Lost tautness
• Lost firmness
• Sank; slumped