is my cortisol really that low?

I recently had some blood tests done and my cortisol came back on the low end at 5.1 mcg/dl. is that really low?  i have been having hypothyroid symptoms for about a year and a half, but my tsh is normal. other results on the low end were prolactin at 4.6 ng/ml, sodium at 139mmoI/L, and potassium at 3.9mmoI/L. my cpk came back on the high end at 277U/L. I recently had a vomitting/diarreah incident for about 6 hours, and I thought it was stomach flu, but also heard about addison's crisis? ????