Unity Maximize lag

Hello there.. im having issues with lag in unity. The problem is when im playing my game without maximizing it in unity it have 200 or 150 fps.BUT when i MAXIMIZE the window it's having something like 30 or 20fps...!!!! Can somebody help me??? im Using Oclussion Culling also! Photo:![alt text][1] [1]: /storage/temp/103591-lag.png