Yes I have had this also, it seems as if you are looking through a kaelidescope and lasts for about an hour. It really freaked me out at first but I realised it is a form of migraine. Most people have this before the pain but like you I never got any pain. However recently I have had some proper migraines believe me it isn't nice. Best thing to get is Immigran from the Chemist, expensive, but will wipe out the pain in half an hour. Leaves your skin felling very sensitive and hot drinks seem even hotter.