Weird Graphic glitch- serious

I have been having servier graphical issues with minecraft since the 1.5 update. I tried to get a screen shot but I couldn't. My minecraft will work fine at first then slowly the problme will start to happen. My screen will start flashing in a way that could cause a fit and everything goes see through with slight parts of colour. This happens on all blocks apart from chests. Minecraft worked absolutely fine before the update. I haven't been playing much single player so I don't know if this is only happening on multi player worlds and it happens most on the survival games servers.
I tried reinstalling minecraft but nothing seems to work. I don't think its my computer as it is very new I only got it 2 months ago and I have checked all of my drivers and my graphics. Please help I can play minecraft any more as I am scared it will cause me damage e.g fits.