A video posted to Facebook Sunday evening showed what is becoming another public relations nightmare for United Airlines, which is owned by United Continental Holdings.

Dr. David Dao boarded a United flight at Chicago's O'Hare International Airport, headed to Louisville, not knowing he was about to be forced to leave a plane that was overbooked.

A nearly 30-second video clip, posted on social media by a fellow passenger, shows three security officers approaching Dao who was already seated, asking him to give up his spot on the plane. After the doctor refuses, he was eventually dragged by his arms and screaming toward the front of the plane.

A witness to the debacle said passengers were warned at the gate that the flight was overbooked, and United was asking for volunteers to switch flights, with reimbursements included. Nobody spoke up.

According to Audra Bridges, who posted the video to her Facebook page Sunday evening, United management came on board the flight and used a computer to randomly select four passengers who would be removed from that trip.

Dao — one of those four randomly selected — claimed he was a doctor and needed to see his patients at the hospital in the morning, then proceeded to say he would call his lawyers.

After being forcibly ejected by three security officers, Dao was able to get back on the plane, though his face was bloody, and he seemed disoriented, Bridges said. United offered no update to the flight's other passengers, who waited for more than two hours for things to calm down before taking off, she added.