Have you ever noticed how your body and mind work better on some days than on others? How one day things come easy to you, but on other days those same things require much more effort? These "off" days have a variety of causes. For example, if your body is stiff or tense, or if you're constipated or suffering from indigestion, your mind will also be disturbed. On the other hand, if your mind is disturbed because you're stressed out or emotionally upset, you may also feel lousy physically.
Yoga helps counteract both the physical and mental factors that give you "off" days. Asanas reduce tension and relieve common problems like constipation and indigestion. They also boost circulation, which energizes both body and mind. Yoga meditation calms the mind, enabling you to let go of worry. Regular practice will definitely reduce the number of "off" days you experience.
So if you're feeling down and out, turn your "off" day into an "on" day by getting into some yoga.