Possible Clues:

• Sound of a sharp, swift or firm impact
• Fall asleep, slangily, with "out"
• Hit the hay hard, with 'out'
• Fall into a 32-Across, with 'out'
• Sedate, in slang
• Fall asleep, with 'out'
• "Let's Make a Deal" non-prize that Gilbert Gottfried appeared in every instance on "Game Show Marathon"
• Knock out
• Fall asleep, with "out"
• Fall asleep, with ''out''