I feel like I most often see this genre refered to as “psychological thrillers”. What you’re describing sounds a little more specific than that, but it’s where I would start. You also might like Enemy (2013). It’s about a man who spots someone who appears to be his exact double in the background of a movie. Things start to become very strange when he tries to find out who he is.
No offense but I don’t believe you or any other onion hater. Alliums and their flavours are in practically every dish of practically every cuisine on the planet. Saying you don’t like onions is like saying you don’t like water.