How to differentiate between love at first sight and infatuation?

If you met someone once and felt something incredibly strong, a sort of tension between the two of you, and cannot stop thinking about that person...it could certainly be infatuation (we tend to convince ourselves it is love...but is it? I wish I knew)....how do you know if you fell in love at first sight or if you are simply infatuated? What if it wasn't their looks that initially attacted you...just some indescribable spark...?