Doctor thinks that in addition to Hashimoto's Disease I also have Addison&#!

I was diagnosed with Hashimoto's Disease a few months ago and was scheduled to see a specialist, which I did monday morning. He sent me for blood work and his office called today and wanted me to come in. The results indicated that my adrenal gland may not be functioning. I go for more tests tomorrow. If it is in fact not functioning he said it would mean that I have Addison's Disease. Both Hashimoto's and Addison's are autoimmune diseases. I am just nervous. The doctor said the meds for Addison's have some bad side effects. Anybody have experience with Addison's? Any info you have would be nice. Thanks