Why is my vision so sensitive to light? I'm experiencing sudden periods of near blindness.?

I'll be sitting in cl, and all of a sudden, the lights in the room will appear to get brighter, almost blinding. It's like my pupils are absorbing too much light. once this happens it is difficult for me to see anything, and nearly impossible to read or function in cl because one line of text will appear to be on top of the next line. (The effect of looking at a light bulb and then looking away, you still see the shape and some of the brightness of the light bulb even after you've looked away.)