We all have/had confidence crises from time to time but your training will help you to overcome that. I'm not sure you want to hear about everyone's worst experiences - that might be counter-productive.
However, the only engine failure I've had was in a Ford Escort at 18:30 on a Friday afternoon on the outside lane of the M25. That was pretty hairy! Thankfully cars can coast along as well.
Cheers
Whirls