I am so sorry you lost you dad so unexpectantly.

It is hard to see people die and I think it is normal replay his last hours but with time, you will begin to think more about the good times then the bad. If he was conscious enough to know you were there, I am sure that was a comfort for him. If he was unconscious (this might be more likely) then he was not in any pain. I think that you made the right decision being there. Lots of hug and prayers that you heal from this traumatic event. Please don't think that you are alone in regards to it being hard to see your dad go through this. It is hard when a parent dies. With time, you are going to heal. Go easy on yourself as you go through the grieving process.