Hi, thank you for asking Healthcare Magic. With this presentation, I would imagine the black out could have been caused by a transient decrease in blood supply to the brain, a condition called syncope. It could have been caused by a tight collar or even turning the head to one side (considering that he was just sitting). Black outs are more frequent when the blood pressure is low than when it is high (except when there are already complications). If he is taking drugs for high blood pressure, it is possible for this to happen. Some other conditions that can cause black outs include cardivascular diseases, shortage of blood, absence seizures and so on. I hope I have answered your query. I wish him well