Trooper Lonnie Haschel said authorities hadn't identified the driver's specific condition but were investigating it as a possible cause of the crash just after midnight near Sanger, about 50 miles north of Dallas.
A language barrier caused investigators to initially believe the driver was telling them another vehicle was involved in the wreck, Haschel said.
The bus left Dallas and was headed to Oklahoma City when it struck the concrete barrier and came to rest on the grassy median, Haschel said. It didn't overturn, but five passengers were ejected through side windows.
The most seriously injured passenger was Raul Peril, whose age and hometown were unavailable. He was taken by air ambulance to a hospital, where he was listed in fair condition and was expected to be released, Haschel said.
Seventeen other passengers were taken to hospitals with varying degrees of injuries. The hospitals declined to release condition updates Saturday. Haschel said he did not yet have a list of the other passengers and was unable to provide their conditions.
Haschel said the bus belonged to Renacimento LLC, of Dallas. After stopping in Oklahoma City, it was scheduled to travel to Little Rock, Ark., he said.
An inspection of the bus uncovered no major problems, Haschel said.
"They found nothing serious that would lend it to be a causative factor in the crash," he said. "The tires were OK, and everything was where needs to be."