My advice to you would be to contact your local surgery and hospital to get all your medical reports for the last 10 years. It cost me £50 and was the best bit of money I ever spent. The more paperwork you send them the better it’ll be. Don’t expect them to contact your doctor, or hospital for information as they just don’t bother. So the more information you can give them make them better informed to make the right decision.
Also, go to benefits and work website, you’ll find a whole range of helpful guides on how to fill the forms out. That’s an absolute must.
Good luck, and don’t let the buggars grind you down.