तद्यथा महामत्स्य उभे कूले अनुसं-चरति पूर्वं चापरं चैवमेवायं पुरुष एता-वुभावन्तावनुसंचरति स्वप्नान्तं च बुद्धा-न्तं च ॥ १८ ॥
In plain words
Picture a great fish gliding along both banks of a river, now the near one, now the far. This person moves in exactly the same way, back and forth between two shores: the shore of dream, and the shore of waking.
Close to the Sanskrit
Just as a great fish moves along both banks, the former and the other, so exactly does this person move along these two ends, both of them: the end that is dream and the end that is waking. || 18 ||