If you lose your health and sense of well-being, you won't make it to work at all. In the long run, it takes far less time to take care of yourself than it does to lose your ability to function well.
One should eat well, exercise, get plenty of rest, have regular physical checkups, and partake in other healthy habits. In addition to the obvious problems associated with ignoring these commonsense health habits, you can see that it's also a horrible waste of time in the long run. Each cold or flu costs you days of productive work time. Who knows how many years of time you will save by simple taking care of yourself?
Take care of yourself – physically and emotionally. You can let go of your fear that you'll fall behind because, in fact, you'll be more productive and have a longer, happier life. So keep yourself healthy – physically and emotionally.