I went through the SAME thing basically this past year.
My dad and i can never seem to get along. and when we fight i would say under my breath "I hope you have a heart attack" or i hope die, and never apologized, but he had been having chest pains and couldn't breath frequently. Well, they had to do an emergency operation this past October, otherwise he would have had a heart attack. The operation was dangerous but nesecary and my dad really thought he wouldn't make it through.
I felt HORRIBLE for all i had said, I thought god, i caused this to him, and what if he didnt make it through? A good friend of mine just said talk to him, he knows you didnt mean it but talk to him. I said things i couldn't take back. So i approached him the night before and said to him you know i never meant what i said when i wished harm on you. And he said i know you didnt. I was once your age too, and said the same things. I apolgoized and that was that./
Even the day of the operation, i was still blaming myself, but some good friends kept my head high nd told me i didn't do anything wrong and shouldn't feel guilty, im a teenager. I saw my dad the next day with tubes coming out of him and him like that really made me realize i didnt mean what i had said. And i kept blaming myself for him being like that.
My dad made it through it well, and is still recooperating but is doing very well. Since then i feel less likely to argue with him (even tho his new medicines do cause him to have some attitudes), its kept me from doing that. He knew i didnt mean what I said, and im sure your dad knew you didnt mean it either.
I'll keep him in my prayers, but you didnt cause that on him at all.