Sri Aurobindo
Letters of Sri Aurobindo
Volume IV - Part 1
The headache and the fatigue is always a sign that the consciousness no longer wants this outward-going thought and speech and 
is even physically strained by it. But it is the subconscient habit that wants to continue. Mostly human speech and thought go on mechanically in certain grooves that always repeat themselves and it is not really the mind that controls or dictates them. That is why this habit can go on for some time even after the conscious mind has withdrawn its support and consent and resolved to do otherwise. But if one perseveres, this subconscious mechanical habit runs down like all machinery that is not kept wound up to go on again. Then one can form the opposite habit in the subconscient of admitting only what the inner being consents to think or speak.