The emergence of my Parkinson's symptoms has caused my body to significantly and rapidly change; it is becoming further from my control and therefore increasingly unable to fulfil my conscious intentions. However, the conscious intentions remain mine alone and I identify with my body as the one I've always been despite the changes.
The pace of change may be much slower in your body but the same issue will arise for you as you get older.
Consider the difference between you as a new born and the person you are now and you will see how much we change. But we still identify that new born as "me"; we celebrate our birth each year.
Heidegger describes our continuing self-identification as an ability to stretch ourselves along between birth and death. Imagine a sheet of plastic was pegged into the ground at birth and we drag the plastic with us as we journey through life. Everything we do, from planning and carrying out specific tasks to recognising ourselves in a mirror, is oriented towards our self-identification.
This has important consequences for me as I inhabit my Parkinson's affected body: I can call upon past experience to guide me (these experiences, despite being in the past, are still mine); when that guidance is no longer helpful I can change it...while staying the same.
No matter what happens I will still be me...