The Origin
The fact that the anger comes with such force is itself enough to show that it is not in you that it is, but that it comes from outside. It is a rush of force from the universal Nature that tries to take possession of the individual being and make that being act according to the will of this outside force and not according to the will of the soul within. These things come in the course of the sadhana because the sadhak is liberating himself from the lower nature and trying to turn towards the Mother and live in her divine consciousness and the higher nature. The forces of the lower nature do not want that and so they make these rushes in order to recover their rule. It is necessary when that comes to remain quiet within remembering the Mother or calling her and reject the anger or whatever else comes, whenever it comes or however often it comes. If that is done, then these forces begin to lose their power to invade. It is easier if one clearly feels them to be outside forces and foreign to oneself; but even if you cannot feel that yet when they enter, still the mind must keep that idea and refuse to accept them as any longer a part of the nature. The idea of the Mother being severe was of course a suggestion that came with the invading force so as to help it to enter. Such suggestions come to many sadhaks (though not so many as before) at Pranam and is the cause to them of much disturbance. Such suggestions must be firmly rejected at once.
How to deal with it?
I think you have always had an idea that to give expression to an impulse or a movement is the best way or even the only way to get rid of it. But that is a mistaken idea. If you give expression to anger, you prolong or confirm the habit of the recurrence of anger; you do not diminish or get rid of the habit. The very first step towards weakening the power of anger in the nature and afterwards getting rid of it altogether, is to refuse all expression to it in act or speech. Afterwards one can go on with more likelihood of success to throw it out from the thought and feeling also. And so with all other wrong movements.
All these movements come from outside, from the universal lower nature, or are suggested or thrown upon you by adverse forces—adverse to your spiritual progress. Your method of taking them as your own is again a wrong method; for by doing that you increase their power to recur and take hold of you. If you take them as your own, that gives them a kind of right to be there. If you feel them as not your own, then they have no right, and the will can develop more power to send them away. What you must always have and feel as yours, is this will, the power to refuse assent, to refuse admission to a wrong movement. Or if it comes in, the power to send it away, without expressing it.
If you find it difficult to reject in the sense of throwing away, what you have to do is to refuse assent. As for instance, as regards voices or suggestions, not to listen to them, not to believe what they want you to believe, not to do what they want or push you to do.
Of course the best way will be if you can keep the contact more with the Mother and her Light and Force and receive and accept and follow only what comes from that higher force. Secondly, to keep the mind quiet, not to allow it to be too active, going from one thing to another. That brings the confusion.
Letters on Yoga — IV, CWSA, Sri Aurobindo.