From p153 of "The Power of Now" by Eckhart Tolle:
"Your physical energy is also subject to cycles. It cannot always be at a peak. There will be times of low as well as high energy. There will be periods of when you are highly active and creative, but there will also be times when everything seems stagnant, when it seems that you are not getting anywhere, not achieving anything. A cycle can last for anything from a few hours to a few years. There are large cycles and small cycles within these large ones...the cycles of low energy...are vital for regeneration."
