What is adrenal fatigue? Honestly curious about it

AF is very real but I don't think most docs know a lot about it & how to treat, unless its Graves or Myasthenia Gravis. I'm pretty sure that stress blew my adrenals out, among other things & nothing but stimulants( which cause me to feel anxious) really work. They only work to give me mental energy. My physical energy has been gone for years. I did take a compound once, yrs ago but it had to be taken 4 times per day and it didn't really help. There was a book written about it but thar was yrs ago. Dont know if there is any new treatment out there. It seemed probable to me b/c no one could ever find the cause of my extreme fatigue. I've been treated for depression, mostly but meds only worked for a short time and now do nothing. Good luck in your search for answers.