See if he responds to his favorite music. There is a group called Alive Inside that has been proving music can bring people around when they listen to their favorite music. Google it. It's amazing...
Parkinson's is another terminal illness which affects muscles & movement. Catatonia is the rigidity of muscles which indicates the messages to his body are no longer being received by his brain. I suggest you prepare for the inevitable, pray for his soul, and seek a support group or counseling if you need help dealing with his death. Hospice can do little good except for comforting you. My best to you and your family.
Daddy had Parkinson's and at the end of his life all he wanted was calm music, quiet toned voices and his morphine drops. I hope you do get involved with Hospice. They "held our hands" and walked us through the end. Daddy was in and out of consciousness and I was so glad to spend a few minutes when he's check back in with us. His passing was peaceful and sweet. I love that one of my final memories of dad was me sneaking out of the family party going on upstairs and sitting by his bed. He asked me to sing to him and I sang all the Christmas songs I knew. He just held my hand for about an hour. Such a sweet memory, just me and my daddy. I guess my answer is: give him quiet and respect. Dying is really a personal business, it's nice if you can give them that. Not always a possibility, I know.
Oliver Sacks' account of Parkinsonian patients in Awakenings is moving and instructive. From what I remember he found that music, as mentioned above, helped in some cases where nothing else did. You can find some short videos on youtube of Sacks discussing his experiences if you look up "oliver sacks parkinsons music"
I guess my answer is: give him quiet and respect. Dying is really a personal business, it's nice if you can give them that. Not always a possibility, I know.