Affiliate Marketing Secrets

I need to get a letter of medical necessity from my doctor so I can get a rolfing procedure done at a chiro/rolfing office not affiliated with said doctor. I need the letter of med. necessity so I can use my health care reimbursement account, pre-tax medical funds taken out of my work pay check, to pay for it.
My question: what sort things should I say to my doctor so I ‘seal the deal’ and get said letter out of him/her? I was just going to talk about my stiff neck and back and my chiro. and spinal health history but I was hoping for some key talking points to make my case.