Answer: It depends only on the upper Light. The power of man’s material vital force also depends on the upper Light, but there is a certain correlation between them.
Question: You often say that there is no fatigue. What do you mean by this?
Answer: There is no fatigue because it depends on how the Light influences you. This is why the power of the life force can be absolutely infinite.
To put it simply, we are created so that we should alternate between being awake and being asleep, but this has nothing to do with fatigue. Certain signals are coming down upon us that make us sleep, make us tired, and make us awake, not because the body needs it.
The laws of nature are arranged this way. It comes from the upper worlds.
From the Kabbalah Lesson in Russian 3/12/17