Definition of vasana from Wikipedia: Vāsanā is a behavioural tendency or karmic imprint which influences the present behaviour of a person. It is a technical term in Indian religions, particularly Buddhist philosophy and Advaita Vedanta.

Before I came to India I had read of such people as Edward Carpenter, Tennyson and many more who had had flashes of what they called “Cosmic Consciousness.” I asked Bhagavan [Sri Ramana Maharshi] about this. Was it possible that once having gained Self-Realization [for the individual] to lose it again? Certainly it was.

To support this view Bhagavan took up a copy of Kaivalya Navanita and told the interpreter to read a page of it to me. In the early stages of Sadhana this was quite possible and even probable. So long as the least desire or tie was left, a person would be pulled back again into the phenomenal world, he explained.

After all it is our Vasanas that prevent us from always being in our natural state, and Vasanas were not got rid of all of a sudden by a flash of Cosmic Consciousness. One may have worked them out in a previous existence leaving a little to be done in the present life, but in any case they must first be destroyed.

(Sadhu Arunachala (A.W. Chadwick), A Sadhu’s Reminiscences of Ramana Maharshi. Tiruvannamalai: Sri Ramanasramam, 1961, 22.)