“What you feel isn’t real,” goes the saying. But a mirror can put an end to that.
Take your mirror from home to the course, as it can be used for all parts of your game.
Place it behind you when swinging in order to check plane and position at the top, or place it on the ground when you putt to inspect your stroke from below.
You can start drawing lines on it if you want to get really technical, to guide your club through the swing.