Hi Manveer,
The coordinates of the Gaze Point data stream and the Fixation data stream are (x,y) points in pixels on the Virtual Screen. This is how the Virtual Screen is described on MSDN:
https://msdn.microsoft.com/en-us/library/dd145136(v=vs.85).aspx
Since (0,0) is the upper left corner of the primary screen, whenever you look to the left or above the primary screen’s borders you will get negative values for the x and/or y coordinate in these EyeX data streams.