You can if your sense of awareness is impaired by a drug, or by some naturally occurring illness or condition.
BTW, would anyone know what injuries this train engineer suffered in the crash? If he had severe head trauma, his loss of memory could be real, but otherwise it's probably a cop-out to avoid serious legal implications.
Yes, injury could certainly cause loss of memory.
I doubt it would cause a loss of the reason why the accident happened, if it was planned, but I could be wrong there.
Do we know the extent of his injuries?