I mean, do they worry what is going to happen to you when they are gone? It's a common fear of the parents of disabled children, especially those who - like myself - don't have siblings who could help them.
My mother expressed her fear in this department several times over the course of the last year. I'm not very independent, on the opposite, I rely on others (my mom especially) in practically every respect, every aspect of my miserable life.
For example, I go with her practically everywhere (I go on my very own only to my dentist, that's ALL) and when we are going out, I have to ask her if I can put on this or that T-shirt/blouse/sweater etc. For example, when recently we were going to go to the grill party organized by our cousin, I needed to ask her if I could wear during it my The Walking Dead T-shirt - something that seems pathetic and ridiculous in case of an adult, even mature-aged woman (42 is not 18) who should be much more independent
What is more, my mother was always very, very overprotective - sometimes which only made the whole situation much worse.