The benchmark Sensex, which opened a mammoth 558 points in red, recovered some of its ground and was trading 100 points down in the negative territory at 16,890 when reports last came in. The Sensex fell to as low as 16,432 points in opening trade, its lowest level since June 1 last year, with a fall of 558 points from yesterday's close. In similar fashion, the Nifty, was trading 35 points in the red at 5083 points.