James Grantz of City Reach Church said the driver told him she had left her blood pressure medication behind, KDKA-TV, Pittsburgh, reported.
Michael Dunne, who was a passenger on the bus with his wife, said the driver's operation of the bus was problematic from the moment she left Philadelphia, that she was driving at high speed on the Schuylkill Expressway, the route out of the city. But she managed to get as far as Bedford, Pa., about 100 miles east of Pittsburgh.
That's when Grantz and Dunne said she somehow got between two tractor trailers on the two-lane Pennsylvania Expressway. Grantz decided he had to do something.
Grantz said he told the driver she had to pull over but she did not respond and appeared "incoherent."
"She was still sitting on the seat. I kind of leaned on her and grabbed the wheel," said Grantz.
Dunne described Grantz as sitting on the driver's lap while steering the bus. He said the pastor managed to get the bus off the highway and into Bedford.
Megabus sent a relief driver, who got the passengers to Pittsburgh 3 hours late Monday night.
"The driver who took ill is doing well and will receive further checks from the doctor," the company said in a statement. "Safety is our absolute priority and, as a matter of course, we are investigating the incident."