What is it, how can you avoid it, and what can you do about it?
I think of burnout as exhausted adrenals: when you've pushed those glands so hard for so long that they can't produce any adrenaline at all at all anymore, you crash. Totally, utterly and completely. It'll take you a day or a week just to get out of bed, and if you abuse your adrenals by, say, drinking caffeine-containing beverages or taking caffeine pills, by smoking, or by getting stressed about anything at all, you crash again. Caffeine, nicotine and stress are all adrenaline stimulants. (I'm sure that I've forgotten one or the other important adrenaline exhauster - please add them in the comments.)
Most of the people I've seen who have had burnout (you don't see them while they're at the bottom of the pit, as they don't have the energy to seek help then) had been overdoing caffeine for months or years before their crash. As their normal cuppa coffee (or similar) stopped working they switched to more coffee, and after a couple potsful a day stopped working they went on to harder stuff (like caffeine fizzies), until they finally popped caffeine pills, possibly by the dozen, just to stay on top of things one more day, one more hour ...
... you know, cemeteries are full of indispensable people.
So think things over: do you really need to be completely and utterly out of the loop for the three years or so that it'll take you to recover from a burnout? Or, er, forget about getting back into the loop. The people that I've seen with burnout have all switched to less draining work, as soon as they possibly could.
Three years is about the time it takes for your adrenals to recover, if you stop all caffeine, all nicotine, and all stress.
Herbs can help you: try licorice root (Glycyrrhiza glabra), real ginseng root (Panax ginseng) (forget about ginseng products, they're usually just caffeine and sugar, and there are cheaper caffeine'n'sugar fixes: try a nice latte, or one of those disgusting caffeine fizzy drinks out there), ginseng leaf (Panax quinquefolius), nettle seed (Urtica dioica), codonopsis (Codonopsis pilosula and other species) (mmmm, codonopsis. Yum!), gotu kola (Centella asiatica), or any of the other adrenal-strengthening herbs.
But herbs won't help you if you don't change your habits. Michigan herbalist Jim McDonald (waves to Jim) said it very nicely: sure, you can put aloe vera on the blisters under the soles of your feet, but don't you think it'd be a good idea to also step out of that sizzling hot frying pan?
Here's a helpful list of caffeine-containing plants: guarana (Paullinia cupana), coffee (Coffea arabica), mate (Ilex paraguariensis), and cola nuts (Cola acuminata) (cola drinks contain caffeine from the cola nuts, and most have extra caffeine added), among others. Tea (Camellia sinensis) and cocoa (Theobroma cacao) contain related xanthine alkaoids. You might wish to go slow on these two, too, while you're recovering.