[weenie]

It sounds to me den that your poor Dad might be suffering from shock.
Which alone is deeply distressing to someone as they relive the event, and by the sound of things that is what your Dad is doing by playing it over in his mind he could be thinking the what if's (example what if I left 5 minutes later) try and get him to talk and reassure him there was nothing he could have done as accidents happen.
Hugs weenie