A feeling of giddy happiness that occurs when one thinks of, looks at, or interacts in any way with a person to whom one has feelings for. Usually impairs one's judgements, resulting in saying or doing stupid stuff.

A crush on someone that is developed in a matter of seconds after seeing them for the first time or learning something about them that makes them attractive.

This is the feeling when you get if you get a crush, listen to something like "My Life Be Like"etc., or see one of those fictional couple gifs.

It could also be considered "present nostalgia".

Your heart also is gonna drive really crazy.