Related Clues:

• Sleeper's concern
• In comics, it's represented by a string of Z's
• Cause of urban pollution
• Shrieking, screeching, etc.
• Soft palate resonance
• Teen music, to some adults
• Breath stoppage, as during sleep
• Nighttime breathing problem
• Subject of a sleep study, perhaps
• Boring event
• Nighttime disorder
• Breathing problem during sleep
• Nighttime noise
• Sound of z's
• Cause of a wake-up