13 am cortisol is not very good. I have a 22 am cortisol (top of range) and I feel like crap.
This is something I think about. Just think about it yourself - if you are in a period of stress and inflammation (ie everyone here!) shouldn't your body be creating MASSIVE amounts of cortisol to battle the inflammation?
With this knowledge, it makes any cortisol test pretty much worthless, you have to go by symptoms. The only way a cortisol test is ok, is if it shows early adrenal fatigue when cortisol is over the top of the range on every reading (am noon evening night) throughout the day. Anything less, and you do not make sufficient cortisol to battle inflammation, because duh, you still have symptoms so obviously your body doesn't make enough cortisol to battle the symptoms.