This may sound strange but I am grateful for having Parkinson's disease. Let me explain. I have a stammer, which can cause huge emotional turmoil and difficulties with forming an identity and a stable inner and outer emotional life. Stammering can become a blinding white light, which can blot out who you are.
When Parkinson's emerged it plunged me into darkness for a while by switching off the blinding white light of my stammer. As such it enabled my eyes to readjust and see the candle light that truly illuminates who I am.
Parkinson's taught me how to see that light; that's what I am grateful for. But you don't need to have Parkinson's to gain this insight; it was just that the light generated by my stammer was so intense that it required Parkinson's darkness for me to see the candle light.
You can turn off the blinding light by acknowledging that the presence of this light is not your fault (you are not responsible for the state in which you are born). Also, there is always something left to do in this life. Within this something there is a choice. Recognising this makes it possible to see the originator of this choice (i.e. you!) and to choose to see the candle light that reveals who you are.