Sri Aurobindo
Letters on Yoga
5. Planes and Parts of the Being
There is a part of the nature which I have called the vital mind; the function of this mind is not to think and reason, to perceive, consider and find out or value things, for that is the function of the thinking mind proper, buddhi,– but to plan or dream or 
imagine what can be done. It makes formations for the future which the will can try to carry out if opportunity and circumstances become favourable or even it can work to make them favourable. In men of action this faculty is prominent and a leader of their nature; great men of action always have it in a very high measure. But even if one is not a man of action or practical realisation or if circumstances are not favourable or one can do only small and ordinary things, this vital mind is there. It acts in them on a small scale, or if it needs some sense of largeness, what it does very often is to plan in the void, knowing that it cannot realise its plans or else to imagine big things, stories, adventures, great doings in which oneself is the hero or the creator. What you describe as happening in you is the rush of this vital mind or imagination making its formations; its action is not peculiar to you but works pretty much in the same way in most people – but in each according to his turn of fancy, interest, favourite ideas or desires. You have to become master of its action and not to allow it to seize your mind and carry it away when and where it wants. In sadhana when the experiences begin to come, it is exceedingly important not to allow this power to do what it likes with you; for it then creates false experiences according to its nature and persuades the sadhak that these experiences are true or it builds unreal formations and persuades him that this is what he has to do. Some have been taken away by this misleading force used by powers of Falsehood who persuaded them through it that they had a great spiritual, political or social work to do in the world and led them away to disappointment and failure. It is rising in you in order that you may understand what it is and reject it. For there are several things you had to get out of the vital plane before the deeper or greater spiritual experiences could safely begin or safely continue.
The descent of the peace is often one of the first major positive experiences of the sadhana. In this state of peace the normal thought-mind (buddhi) is apt to fall silent or abate most of its activity and when it does, very often either this vital mind can rush in, if one is not on one’s guard, or else a kind of mechanical physical or random subconscient mind can begin to come up and act; these are the chief disturbers of the silence. Or else the 
lower vital mind can try to disturb; that brings up the ego and passions and their play. All these are signs of elements that have to be got rid of, because if they remain and other of the higher powers begin to descend, Power and Force, Knowledge, Love or Ananda, those lower things may come across with the result that either the higher consciousness retires or its descent is covered up and the stimulation it gives is misused for the purposes of the lower nature. This is the reason why many sadhaks after having big experiences fall into the clutch of a magnified ego, upheavals, ambition, exaggerated sex or other vital passions or distortions. It is always well therefore if a complete purification of the vital can either precede or keep pace with the positive experience – at least in natures in which the vital is strongly active.
Current publication:
Sri Aurobindo. Letters on Yoga // SABCL.- Volume 22. (≈ 28 vol. of CWSA).- Pondicherry: Sri Aurobindo Ashram, 1971.- 502 p.
Other publications:
1. 10099.
Sri Aurobindo. Letters on Yoga. I // CWSA.- Volume 28. (≈ 22 vol. of SABCL).- Pondicherry: Sri Aurobindo Ashram, 2012.- 590 p.
2. 20452.
[Largest or earliest found passage: ]Sri Aurobindo. Letters of Sri Aurobindo: In 4 Series.- First Series [On Yoga].- Bombay: Sri Aurobindo Circle, 1947.- 416 p.