Are you so in love that you act like a lunatic? Does the full moon make you howl? If so, you’re moonstruck! Moonstruck literally means to be affected by the moon, but moonstruck people are dreamy and in love.
You can use the adjective moonstruck to mean "insane" or "loony" in general, but it's most often connected to the idea of being lovesick or romantic and irrational. It stems from an ancient belief that the moon could actually cause insanity. The first written use of moonstruck is found in John Milton's 1674 epic poem "Paradise Lost," included in a list of humanity's afflictions caused by original sin: "moon-struck madness."