Three crew and two passengers were taken to hospitals and treated after the plane landed at Billings Logan Airport in Montana, said Christen Davis, a spokeswoman for United.
Spokesman Luke Punzenberger said both passengers and two of the flight attendants were released Monday, while the third flight attendant remained at a hospital.
"I think they were somewhat panicked," said passenger Bill Dahin, who said the flight attendants seemed surprised at the jolt. "I think they were trying to assess things themselves so they really didn't offer any explanation because of what happened so quickly."
Dahlin said the plane dropped sharply, without warning, as it began its descent into Billings. One woman, he said, hit her head so hard the ceiling panel above her cracked.
"There was a lot of screaming, a lot of hollering," he said.
The flight, 1676, had 114 passengers and five crew aboard.