Related Clues:

• Chemically nonreactive
• Like some batteries
• Dull, as a party
• Phlegmatic
• "In the Dark" band's nickname, with "the"
• Couchbound, perhaps
• __ ringer
• Utterly lethargic
• In need of charging, as a cell phone
• Defunct
• Breathless?
• Beyond tired
• ___ as a doornail
• Very, very tired
• Chemically quiet