Is expiation obligatory upon a driver who was driving at a normal speed, momentarily lost consciousness, causing the car to overturn and one of the passengers to later die due to injuries sustained in the accident? And what is the expiation in this case?

If a driver feels faint but continues driving, he is sinful and responsible for the consequences of any accident. However, if he only feels faint at the moment the accident occurs, there is no blame upon him, as it is beyond his control. It is a condition that the driver takes all safety precautions; otherwise, he will be held responsible.