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According to the National Enquirer, the actor was seen sleeping while standing backstage at a Save the Children fundraiser in Greenwich, Connecticut.
A source said: "Someone asked him if he was okay, and Matt woke up.
"He explained he recently found out he can nod off on his feet."
Damon, who is expecting his fourth child with wife Luciana this fall, recently said that the couple are feeling the stress of their pending arrival.
