You're a shy person who's into petplay, and so you've bought an invisible collar to wear in day-to-day life. When you see your roommate later that day, the collar turns out to have a bit more magic than you thought...

Playing around with unaware/reality shift kinda sorta. Is this technically dubcon because the roommate didn't consent? Oh well, still in the top 10 least-evil unaware hypnosis stories.