It is a real thing, except that it is NOT love.
Love takes 2 years or more of living together before it even STARTS to grow.
Love at first sight happens when you have some serious repressed issues/pain that you are not consciously facing. So when you encounter someone whose subtle signals suggest they will trigger your pain, your brain releases chemicals that instantly and strongly attract you to the person.
Chemicals that make us feel "high", and what we are "in love" with is our "high". The other person only triggers this.
Unfortunately the brain will eventually go back to normal, the "high" dies out, and THEN the person starts triggering all of our buried pain.
Our brain seeks out what it "knows" .. so if there is buried pain that is what our brain seeks out in others. And the stronger and more-quickly we "fall in love", the worse the outcome is going to be.
People who are psychologically well-adjusted .. well, the girls take about 6 months of steady dating before they START to be serious about the other person. And guys take about 12 months.
Anyone who "falls" hard and fast .. get away as soon as you can. Unless you enjoy relationships that become painful.