Possible Clues:

• Terrifying experience hit German badly
• Frightening prospect arming the jerks
• Men, a girth getting out of control is a nasty experience!
• Amount, by the sound of it, of unpleasantness with 3 down
• Frightening dream
• What a horrible amount of darkness, perhaps
• O, to dream of her fills my heart with horror! (9)
• Dream of a dark horse
• You'd never dream of making light of anything so unpleasant
• No steed is welcome if it's so dark as this