Being turned into an inanimate object and basically forgotten is Izzy's worst fear. It's been mentioned before but it relates to her experience in the hospital. Just the idea of being unable to move and thinking what if this is the day nobody visit but taken to its logical extreme. 

Though she could've had that other dream: the one where she turns into a moth or butterfly. If you stacked all these dreams together, I'm not sure there's enough ice cream the synthesizer could make that would help Izzy feel any better.