Possible Clues:

• Sank under pressure or tiredness
• Went south, in a way
• Slumped
• Flopped down with horse at the rear in Fairyhouse - overall it's unfortunate
• Succumbed to gravity
• Sank, subsided
• Unhappy about rising soufflé ingredient – sank in the middle!
• Hung down loosely
• Artist returning without painting finally dropped
• Ran out of bravado