Giving up all its early gains, the Sensex at the Bombay Stock Exchange stood 154 points, or 0.9 percent in the negative zone, and slip below the key 18,000 mark, at 17,883, in afternoon trade, a short while ago. The Sensex fell as investors offloaded especially interest-rate sensitive stocks, on fears of a further rate hike by the Reserve Bank of India, and amid weak regional bourses. In the morning, however, the Sensex had opened a good 104 points, or 0.6 per cent higher, at 18,142. In the other Asian bourses, key benchmark indices in South Korea, Indonesia, Hong Kong, Taiwan and Singapore were down by between 0.2 percent and 0.5 percent.