The duaa for general sickness is :
“As alullah al-'azheem rabb al-'arsh al-'azheem an yashfeeka”
“I ask Allah the Supreme, Lord of the magnificent throne to cure you.”
Our beloved Prophet Muhammad s.a.w. said that when this du’a is made and the end has not yet come for that sick person, than that sick person will be cured, Insha’Allah.