What does this mean...

So tomorrow AF is due and I decided to test today. I took the test ( cheap dollar store test don't like wasting money) I also have used them in the past and they have worked fine. Anyways. Took the test seen the first line and thought hummm...that's the pregnant line...look at the box and it was. Looked back at the test and that line was gone and the normal line (negative line) was there. Guess my question is. Has anyone every experience something like this where the pregnant line disappears after it pops up. Guess it's retest time.