Sri Aurobindo
Letters of Sri Aurobindo
Volume IV - Part 3
It is inevitable that in the course of the sadhana all sorts of conditions should come through which one is led towards the fullness of the true consciousness. You are now, as are most, in the physical consciousness and its principal difficulty is externalisation and this covering up of the active experience so that one does not know what is going on inside or feels as if nothing were going on. When that happens, it means that 
something has come up, some part or layer of the physical, which needs to be worked on and, when that has been done,– it may take longer or shorter,– the conscious active inner experience recommences. The muteness in the mind is not a bad thing in itself, it is a favourable condition for the working. Also what you describe as taking place in the head, must be the working of the Force there,– it sometimes gives the impression of a headache. There must be a working in the physical mind to get rid of some difficulty or else to prepare it better for the admission of what comes from above.
It is necessary to have a great patience – so as to go through these conditions and not get apprehensive or restless – and a confidence that all difficulties will be overcome.