Adrenal Fatigue is not a term used in conventional medicine. It is a layman's term often erroneously used to describe physical states that have nothing to do with the adrenal glands (I'm tired therefore it must be adrenal fatigue). It is for these two reasons (not a term used in conventional care and misused by laypeople) that it could be considered bogus.
➤ low hormone production (measurable) from the adrenal glands
➤ causation of hypofunction preceded by taxation
Both sections produce hormones in response to stress mediated by the sympathetic nervous system. More stress = more hormone production. This point is not controversial. This means that stress, induced by situation, emotional state, illness, and/or stimulants, requires increased function and that high levels of stress induced output may result in deficit by taxation (aka adrenal fatigue).
Chronic low production of adrenal gland hormones is called Addison's Disease and it is not caused by over-stimulation or taxation. However, can there be low production of any adrenal gland hormone without it being pathological? In other words, can there be a sub-clinical drop in adrenal gland function resulting in one or more adrenal gland produced hormones to fall below optimal levels? The answer is absolutely yes. Can this drop follow or be caused by over-stimulation of the sympathetic nervous system? Also, absolutely yes.
These hormone levels can be tested by labs. DiagnosTechs, for example, offers an Adrenal Stress Index that is very detailed. There are many tests for abnormal function that the average MDs are not using or know nothing about, which doesn't mean the conditions don't exist. Abnormal hormone levels will result in symptoms to the patient but, unless the doctor is trained in corrective physiology (sometimes referred to as Functional Medicine), the symptoms will be treated not the cause (the untrained MD knows nothing about repairing or improving the function of almost any system).
Let's take, for example, cortisol. Consumption of stimulants will result in an increased production of cortisol. High intake of stimulants will eventually lead to exhaustion. This spike and drop can be measured through saliva tests and validated medically. However, the term Adrenal Fatigue is never be used. It is referred to as high or low cortisol levels. In this case the term Adrenal Fatigue is technically correct even though the term is not used conventionally.
Keep in mind that the adrenal glands produce many hormones that direct functions throughout the body. When cortisol levels increase there is resulting decreased activity in the immune system (collectively). The brain has to balance the hormones and their effects. If the body needs greater immune system performance there will be a decrease in cortisol levels. This is a great example of low energy, due to low cortisol, that has nothing to due with "adrenal fatigue." This is a strong argument against the term adrenal fatigue by conventional care doctors because if there is a low hormone level it may also be due to the body adjusting various functions and not due to taxation.
Adrenal Fatigue, although sometimes an accurate description, is a terribly misused term. Guessing or generalizing about your health is never a good idea when there could be serious issues needing treatment. It is also important to be cautious when taking "adrenal supplements" that may cover up what the root cause of the symptoms. When in doubt, seek a doctor trained in corrective physiology.