I'm not 100% how i got stuck in sneak, But I'm pretty sure I tried to stand up while rolling, in first person, using a bow. That or entering a room with a fully drawn bow in first person, zoomed in. One of those cause me to get stuck in a sneak/not sneak hybrid
Your interface is as if you're standing- People will see you if youre not sneaking (the eye doesn't pop up), but you attack/run/stand/walk in sneak mode.
To get rid of this simply save, and load state.