false positive?

Okay so I took this test last night (March 18th) around the same time (9:30 pm) and it was clearly negative. But I thought I might just take it out of the trash and check it again tonight (March 19th) and I saw the other line...is it possible for it to change over night? Or to be a false positive? Has this happened to anyone else before? I just stopped my period on the 16th and it was definitely a normal period. I'll probably retest in the morning with a digital test but I wanted opinions before I took another test