An illness caused by sudden onset of feels, specifically the Ls. Symptoms include butterflies, daydreaming, lightheadedness, and growing attachment to the individualresponsible for this illness. More often than not, it sneaks up on the individual. Symptoms increase when both individuals share the same illness.
A moribund metaphor meaning "out of control in love." But, think about it. Aren't you head over heels every day? Shouldn't it be "heels over head in love"?
"I'm absolutely head over heels for you."
"You're delusional."
"Call it what you will, I think its the best feeling in the world."
"Yeah I'm pretty sure I know the feeling."
"<3"