how many times has this happened on camera?

Cheney falls asleep during Cabinet meeting on wildfires.

During a cabinet meeting yesterday, Vice President Cheney fell asleep on camera while President Bush was discussing wildfires in California. A Cheney spokeswoman “laughed it off,” telling CNN that the vice president was “practicing meditation.” CNN’s chyron reported that Cheney was seen “meditating” — rather than sleeping — during the cabinet meeting.
(Think Progress)
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And considering the number of times it has happened on camera, how many times has it happened that we haven't known about?
Is this loon still able to function as a VP? (Though, thinking about it, maybe it would be better if he slept through the rest of his term - maybe he would do less harm that way!)

Crooks and Liars agrees and has many screen shots