How to make sure characters act accordingly when a spell that clouds judgement is cast on them?

If an NPC spellcaster, or any other magic source, magically clouds the judgement of a PC, how can I make sure the player acts according to the spells nature? Is there anyway to do this without seizing their character? My specific example is, in d&d-5e, if the spell Enemies Abound, which makes the target perceive all creatures as enemies, is cast on a player, how can I encourage them to choose targets indiscriminately? Would I have to control their PC, or could I allow them to remain in control?