Sri Aurobindo
Letters of Sri Aurobindo
Volume III - Part 4
Some have this swaying of the body when the peace or the Force begins to descend upon it, as it facilitates for it the reception. The swaying ceases usually when the body is accustomed to assimilate the descent.
The peace comes fully at the meditation time because the Mother’s concentration at that time brings down the power of the higher consciousness and one can receive it if one is able to do so. Once it begins to come, it usually increases its force 
along with the receptivity of the sadhak until it can come at all times and under all conditions and stay longer and longer till it is stable. The sadhak on his side has to keep his consciousness as quiet and still as possible to receive it. The Peace, Power, Light, Ananda of the higher spiritual consciousness are there in all veiled above. A certain opening upwards is needed for it to descend – the quietude of the mind and a certain wide concentrated passivity to the descending Influence are the best conditions for the descent.