Perception of Karma

A sign of spiritual exertion, however, is this: that one feels—the brain is used up. It is just as we may feel that a demand has been made on the muscle of the arm when lifting things. Ordinary thought makes no such strong claims upon the brain. The process continues, and you will even notice that when you try it for the first time, the second, the third, the tenth, you get a slight headache. It is not that you get tired or fall asleep; on the contrary, you cannot fall asleep; you get a slight headache from it. Only you must not regard this headache as something baleful; on the contrary, you must take it as actual proof of the fact that you have exerted your head.