This is how to tell the difference between exhaustion and burning out: you get exhausted if you pushed hard, you burn out if you pushed hard for a wrong reason. If someone claims they can fix burn out by taking a walk or a getting a nap, they're not burnt out. You are burnt out when having hard time not just doing your work, but also when trying to recuperate. Basically, that "wrong reason" depresses you, making recovery very hard. If you are lazy due to overall fatigue, the next day you'll go back to work like it never happened; if you burnt out, the "next day" never happens.