The Bombay Stock Exchange benchmark Sensex today rose by almost 13 points in early trade. However later it lost its initial gains and was trading at 17995, down by over 5 points when reports last came in. Similarly, the wide-based National Stock Exchange index, Nifty was up by 4 points to 5,401 points. Analysts said the fall in Sensex is due to funds and speculators who kept their positions restricted on last session of monthly expiry in the derivatives segment.