Low cortisol levels, esp chronically suppressed, render the body maladaptive to stress - from physical exertion to mental capability of coping with anxiety, mania and a number of other disorders. There is evidence of insufficient glucocorticoid signaling in stress-related neuropsychiatric disorders. Impaired feedback regulation of relevant stress responses (CRH, ACTH, Cortisol), especially immune activation/inflammation, may, in turn, contribute to stress-related pathology, including alterations in behavior, insulin sensitivity, bone metabolism, and acquired immune responses.
However, one thing with cortisol checking - it should be monitored on a consistent basis - levels are highly variable within even a short span of time. Low chronic cortisol is usually attributed to post traumatic symptom disorder, so....think about it...
I am not sure about DHEA - it's very abundant to begin with as it serves as a precursor to androgens and estrogens and usually DHEA has inverse relationship with cortisol which might explain its acute elevation; sometimes it is implicated in adrenal tumor, but that is something I would let your M.D. to hypothesize