I thought I was burning out pretty hard core recently. I went to the dr, did some blood work, and found out I had a serious vitamin D deficiency causing all sorts of scary symptoms. Might be something to look into if you're working too much and are experiencing new health problems.
I had a manager that forced me to take a day off at least once a month and I still owe them for that. I dont do it every month now, but I definitely take the time to rest more often and in the end I am much more productive.