The higher the Gap up today, the mor confident I shall be to sell on the first tick. There is one stop NIFTY missed in this pilgrimage downhill: "21800". When she realizes it, she would turn around and rush to make that final downward journey before continuing up to where she belongs.
A gap down opening is when things will become tricky. In this case there might or might not be a retracement to gather longs before falling.