Hi there - I just wanted to say sorry to hear you are in this situation as I know how soul-destroying it can be dealing with DWP.
The thing that has helped me with benefit claims is googling the benefit you are on and the decision makers handbook, for example "DLA decision makers handbook"
This gives you the criteria that you will be judged on and that will help you to know how to describe your illness to them in the right way. You do have to trawl through a lot of stuff to find it.