Eyes change colour painfull too?

ive had this problem........4 years? but never noticed that my eyes started changing colour when it happened. when i stand up i get light headed and a white light forms in front of my eyes its got so intense once i fell over also my pupils go really small but just before i noticed my eye colour (green) went a lighter colour and then when the symptoms went my pupils went back to normal and i seen the colour in my eyes go back to green? to describe my pupils its light siting in a dark room then someone turning a bright light on.