Uncontrolled movement during fights

Ok, so I'm playing and everything is fine... then i get into a battle 1v1 or team, and the hand cursor turns to a sword by itself and I lose all control of my champion. Any kind of clicking in another direction does not work. My champion becomes infatuated with the enemy and will follow them into the depths of hell, and sometimes under turrets. This is creating a lot of unnecessary deaths for me while playing and is quite frustrating. Anyone who can, HELP ME PLEASE ;(