Took a test & was negative & then when I looked an hour later it was positive?

I took the pregnancy test & watched it for a min & went into the other room to get my 2yo. out of bed and changed his diaper. I walked back into the bathroom and it was still just one line. It was at least 3 min (test says 1 to 3min). The test at this point was just negative so I tossed it in the trash. An hour later I went to the bathroom and I pulled it back out and it was positive. I'm not sure what to think at this point. Has something similar ever happen to anyone and it turn out to be that they were in fact pregnant? I am def going to retake tomorrow.