Related Clues:

• Failed as a sentry
• Went out
• Was out
• Was an awful security guard
• Rested
• Was in the arms of Morpheus
• Was out for a bit
• Reposed
• Snoozed
• Sacked out
• Pulled a Van Winkle
• Failed as a night watchman
• Went undercover?
• Drifted off
• Used a hammock, perhaps