Is the questioner considered disobedient to his father, and what is the expiation for his sin, after he shouted at him and uttered inappropriate words due to his father's refusal to take medicine and his stubbornness, knowing that he performed his duty of serving him perfectly until his death?

May Allah عز وجل improve your solace regarding your father, and we ask Allah for His mercy and forgiveness upon him, and that He raises his ranks and expiates his sins through this illness, and that He records for you the reward for your service to him. Your shouting at him and uttering inappropriate phrases is a grave act of disobedience, especially since the Shari'a has emphasized filial piety and patience with parents in their old age. Your remorse for this behavior is good, but it is not enough. Rather, sincere repentance is obligatory, and you must continue to honor him after his death.