Passengers claim the Men in Black II star started behaving strangely halfway through the ten-hour British Airways journey from Los Angeles to the capital's Heathrow Airport.
But they were stunned when she stripped off her clothes and tried to climb into the bed of a sleeping stranger, reports British newspaper The Mail on Sunday.
Boyle's publicist Sarah Culliver says, "It genuinely is completely inconsistent with her character and behavior."
A British Airways spokeswoman confirms, "First-class passengers on board Flight BA 282 from Los Angeles to Heathrow reported that a female passenger in the cabin was behaving strangely."
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A shocked witness adds, "People recognized she was Lara Flynn Boyle and saw her popping pills on board early in the flight.
"She was starkers, woke a passenger up, tried to get into bed with him, pulled open the blind and said, 'We're landing, get your clothes on,' even though we were more than four hours away from London."
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