Kaila ........you just reminded me. I was given a key last night as well! I knew there was something important I had to remember! Thank you for your post!
One of the great things about dreams and symbols is that there can be more than one interpretation. Ultimately, there is a part of you that knows the answer for this dream is a message from your higher self.
As to the actual key, that is amazing. I've been hearing many stories of things showing up unexpectedly - and yes, things can simply appear. One theory is that we are shifting realities and that the boundaries between realities (such as the waking and dream state) are becoming thinner and thinner. So objects from one reality can move into another. Lots of people have been mentioning about objects disappearing and then reappearing.