(CNN) -- Tom Wagner woke up Friday night and the plane cabin was dark. And empty. Completely empty.
He looked around from his window seat near the back of the jet and wondered, "What is going on?"
He tried the jet door. It was locked.
He told CNN affiliate KTRK that he called his girlfriend, and she thought he was kidding, or crazy.
She called United Airlines and about 30 minutes later, the door opened up.
"I was coming from Louisiana to see my sister in California. We had a layover in Texas," Wagner told the station. "I just took my hat off and I took a nap."
Well, he must have been very, very tired, because as the three dozen other passengers deplaned after a one-hour flight, he dozed.
As the flight crew left the plane, he slept.
"What if I had a medical condition or something? What if I had a heart attack and I was dead? You just shut the plane and leave someone on there? It's the way I look at it," Wagner said.
Wagner stayed in a hotel room, on the airline, before flying to California the next day. He said United gave him a $250 voucher.
The flight was operated by ExpressJet, a United partner.
"ExpressJet is investigating to determine how this occurred. We sincerely apologize for the inconvenience this caused for the passenger," the carrier said Saturday in a written statement to KTRK.
ExpressJet told KTRK there was a post-flight cabin inspection, but the company couldn't explain how Wagner was overlooked.
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