Wed Sotah 2

Tosfos quotes the Yerushalmi. The Pasuk says that a spirit of jealousy cam over him. (This implies that he's Mikane in a serious spirit) Therefore, someone is only Mikana with fear and not with lightheadedness or haughtiness. The Torah writes by these laws "Chuka" which implies that it's totally necessary (and any other type of Mekana doesn't take effect.)