so im walking through a forest and theres a wooden door ahead. just a door. and i walk through it and the door leads to a castle looking hallway lit with torches and made of cobblestone. along it are just doors. i walk through the hallway ant it opens up into the... lets call it a throne room. on the throne in the middle of the room is a woman with three heads. she hands me a key and i go to one of the doors in the hall. i unlock it and open it and a dog runs at me and jumps. then i wake up. does anyone have any idea what this means?
It means that your subconscious was recalling imagery of a forest, and a door. But since your conscious has some very small play within a dream, it tried to make sense of what was going on, attempting to predict what could be associated with the images.
Where do doors go? Hallways. In the midst of reorganizing your long-term memories, tropes, and archetypical knowledge to file away new information and discard the unnecessary, your hippocampus recalled a hallway, which happened to be a castle. But you didn't know where you were or for what you were looking.
So what's in a castle? A throne room with royalty. And there they were. The doors, though, had seemed a curiosity, still in your short-term memory, and your conscious mind wondered where they went. But are they locked? A key!
The key, naturally, opened the first door you encountered, without having to figure it out (I'd almost be willing to bet that the mere concept of having the key enabled the door to open). Where does that door lead? You're indoors, so possibly outdoors? What's outdoors? Dogs!
You experienced a hypnic jerk and woke up.
Sometimes a dream is a dream. Rarely does the subconscious fabricate imagery; often concepts and tropes are meshed together, and the part of your brain active enough to interpret the dream (you do not dream in the deepest part of your sleep, rather only when approaching and when leaving the deepest parts of sleep, and the REM stage -- rapid eye movement, the dream state -- lasts longer after the deepest portion of sleep) into something that makes more sense.
If you believe the dream has some deeper message, it is not something anyone but yourself can answer. The meanings lie within your subconscious, as that is there origin whether they are images and concepts dredged from deep memories, or whether you believe they are messages from the astral or an outside entity.