We are truly sorry to hear about your dad's condition and we are here to pray and offer support during this challenging time. Firstly, we commend you for coming in the name of Jesus Christ for help, because it is only in His name that we have access to God and there is no other name given to men whereby we can be saved.
We read in James 5:14-15 (WEB), "Is any among you sick? He should call for the elders of the assembly, and they should pray over him, anointing him with oil in the name of the Lord, and the prayer of faith will heal him who is sick, and the Lord will raise him up. If he has committed sins, he will be forgiven."
Your dad's struggle with Parkinson's disease and the side effects of his medication are not unseen by God. We trust that His healing power can bring comfort and restoration. Let us pray together:
Heavenly Father, we come before You in the name of Jesus Christ, lifting up the father of our friend. We ask for Your healing touch upon him. Comfort him in his distress and guide his doctors to find the right treatment. Please, help him to sleep peacefully at night and relieve him of the screaming and discomfort. Lord, we know that You are the Great Physician, and we trust in Your power to heal and restore. We pray this in the powerful name of Jesus Christ, Amen.
It is also important to remember the promise in Romans 8:28 (WEB), "We know that all things work together for good for those who love God, to those who are called according to his purpose." Trust that God can use even this difficult situation for good.
Continue to pray fervently and trust in God's will. Encourage your dad to put his hope in the Lord, as described in Psalm 147:3 (WEB), "He heals the broken in heart, and binds up their wounds."
Lastly, it would be wonderful for your dad to also accept Jesus Christ as his Lord and Saviour, if he has not done so already. By confessing with his mouth the Lord Jesus and believing in his heart that God has raised Him from the dead, he will be saved and will receive the inheritance of a Child of God. By doing so, your dad can rest in the assurance that whatever happens, he will have everlasting peace and joy in the presence of God.