Sant Maharishi Mehi:

 

The stream of celestial nectar is flowing from the
subtle canal of the sushumna nerve. Like a fish the
consciousness current is moving upstream.15 Like a
fish making its way upstream, the mind travels with
consciousness away from the senses (the current) with
great difficulty. (This will seem to the mind a difficult
and “unnatural” course, as the mind is habituated to
move toward the senses and the sensory objects.)