Depends on the level of burnout.
If I find myself burning out I usually take a break and do healthy things. Exercise, eat healthy, I try not to stay still or lie in bed cause then it just gets me stress and I feel unproductive and gross.
However if I superbly burn out, what can happen is I don't give myself time to recover and so I'll have scattered burnouts all throughout the week, if I have this pattern I'll just stop for a week or two, take unpaid vacation from work and just relax for a week. That's only happened once (and it was when my partners brother was murdered, so it takes a LOT to get me to that state).