How to deal with a sick parent/ loved one?

I don't really know what to say. I'm 22, the oldest of 4 kids. My dad has been in hospital for about 7 weeks fighting an infection, on antibiotics. He was wallking, talking, breathing fine. Nobody really thought anything of it. But the night before last we received a call from the hospital to say he was critical and we had to go in straight away. Basically, we got there and thought he wouldn't make it through the night. Thankfully he did, and yesterday he was awake on a ventilator. It was the most difficult thing to see him struggling so much on it. Mouthing to us all that he loved us. Then when the nurse asked him if he was tired, he nodded and she said she may sedate him again. All of a sudden, he squeezed my hand, eyes wide open, shaking his head. He thought if he went to sleep he would never wake up again. That was the most horrible and horrific moment of my life. We had to leave after visiting times and he apparantly became very agitated and they had to sedate him. The horror of them doing that to him (even though i know it was best), torments me because of how he felt beforehand..... Anyway, now he was rushed to a specialist hospital and he's having an emergency operation in the morning to replace a heart valve. I'm out of my mind with worry, i constantly feel sick, i can't sleep, i can't eat.... i'm thinking of the worst scenarios.... Can anyone please give me any help or guidence on how to deal with a situation like this.