Keep touching the work.

Work that is touched regularly stays warm. It keeps turning over somewhere below conscious thought, and you return to find that a problem has partly solved itself. Work that is left alone goes cold, and the cost of restarting is not the lost days but the loss of everything you were holding in your head about it.

On the days you have nothing to give, still open the file. Read the last paragraph, look at the last decision. Five minutes of contact preserves something that a week of absence would take from you.