Wait until tomorrow to take a day off when you are ‘not feeling it.’

When you feel tired or worn out, still go through the motions.
Get out of bed, do the workout, and project to the best of your ability.

Decide that you will take a day off tomorrow.
These feelings could mean you need a day off, but not today.

Take the day off if you wake up the next day feeling like you need a break.
Chances are you will realize that the desire to rest was just weakness, a temptation to take the easy road.