Possible Clues:

• Hypnos's realm
• Coleridge called it 'a gentle thing'
• Hibernation
• Do a Van Winkle
• 'A gentle thing,' said Coleridge
• Nighttime refresher
• Nocturnal ambition
• Catch forty winks
• Looking back, removes skin to hit the hay
• Virgil called it a gift of heaven