Dreaming of closed doors symbolizes missed opportunities or opportunities that are denied or not available to you. Someone or something might be blocking your progress. But it can also symbolize the ending of a phase or a project you've recently embarked on. Being locked inside like you suggested represents harsh lessons that need to be learned. Don't know if any of that applies to you but I got it of a website called Dream Moods. I look on there myself sometimes when I have a confusing dream because it isn't anything superstitious but just makes plain sense. Hope that's helped you somewhat!