I don't know what type of work you're in but transitioning back into the work place after extended leave can seem daunting. You've been through a lot and in the "ideal" world .... You'd be given some leeway into your transition back .... But this is not always the case.

Are you saying your work know the reason why you were away ie your diagnosis? I'm going to be pretty upfront and let you know from my own personal experience that doesn't work well, regardless of being casual or permanent .....