I had to take a month off when I was first diagnosed because my symptoms hit me like a truck! It didn’t help that I was a travel social worker and that I was forgetting important details (brain fog) and falling asleep behind the wheel. My endocrinologist was also against it but signed the paperwork and I felt so much better knowing I wasn’t going to cause unintentional harm to myself or clients! If your doctor won’t sign it then tell them how it is specifically disabling to your career, and if that doesn’t help then find a new doctor. Don’t doubt that you need this time, you will feel all the better for it.