Why Does The Text On My PC Screen Go Blurry At Times :'(?

Please help! It's getting annoying now. I'm trying to use my PC when suddenly I find the texts become blurry as if I set it to a low resolution. But I've always checked it and it's fine, but the text remains blurry for a while then returns to normal again. This happens only occasionally, but it doesn't really bother me, but the times when I have something really important to do; it messed up, causing my frustration. :'( Even typing this up right now it's STILL blurry! Please help? :')