Sometimes the curry becomes spicy & there is no point adding salt 
or sugar.
Try this
Boil (cook ) few baby carrots in microwave - it takes about a 
couple of minutes to cook, after they have been cooked mash them 
finely & add to the gravy !!
The gravy will taste wonderful & the spicyness will be reduced 
instantly by the sweetness of carrots & will also add some 
consistency to the gravy:)