i have this problem somtimes when my ocd is getting the best of me. I can't stand it!!! It will convince me that I am going crazy. I get these weird feelings when I look at things sometimes and then I think "OH GOD!, Here it comes. I've finally lost it". I think it partially ocd and partially the anxiety that comes from it. And if you've ever experienced derealization then this thought of "nothing is real" is quite common. Well for me anyway. You know it is a completly rediculous idea, but you cannot help but think about it and think about why your thinking about it. Then you end up thinking so much that you tire you brain out and end up more confused than you origionally where.
well it's not really normal...but haven't you ever seen the matrix? that movie alone shows you're not the only one who's had this kind of idea. you really should see a psychiatrist. these thoughts aren't uncommon for someone with ocd and they know how to help relieve them. do you already see one?