I'm going to humor this and provide an actual argument, instead of the "lulz" I've been posting...
Let's take our life to be a dream. If all is but a dream, what must be necessary for everything to actually be a dream? Well, certainly something must exist, for the dream itself wouldn't exist without existence. So we have at least, an existent dream. If it is reasonable for the dream to exist, then I think it reasonable for other things to exist as well, for a dream by itself isn't much of a dream without contents. You can't have a dream purely about nothing. You can dream about the color black, where nothing happens in your dream but you see the color black, but then at least 1 other thing exists, the color black. Someone might say "well, the color black isn't really a color, so much as an absence of color, so you're not really seeing anything." To which I would respond, you are still recognizing the lack of something, which means that something is in fact going on. Maybe these things only exist within the dream, but they still exist since they exist within the dream.
Taking these to be true:
-the dream exists
-other things exist, at least within the dream
-reality consists of all real things
Now I ask what it would mean to have a dream but no dreamer. We have now, some sort of metaphysical existence, but no lower existence to base it on. Now, where precisely are the things that occur in the dream going to come from? Perhaps they can just spawn somehow through some sort of godly power, and the dream goes on, but if this dream is the foundation for all things, then it isn't really a dream at all. Since this dream exists, but other things outside the dream do not, it's a foundation of sorts for all reality, and essentially, it's own reality.
If there is a dreamer and a dream, there is naturally still some existence. This differs slightly, because in this case the things in the dream are going to come from the realm of the dreamer, unless someone has ever dreamt up something that doesn't exist, which would be something without color, without mass, without some form, concept, or idea. This I find highly unlikely, but if proven otherwise I would be forced to change the results of this proof. Though, it may be impossible to prove since describing the thing in terms of our language would be to describe it in terms of things which do exist, and if it's describable in terms of existent things, then it isn't unexistent. If the dreamer exists, then his realm is the reality, and the dream is precisely a dream, or unreal, however you wish to call it.
So, we have two cases, the dream and no dreamer, and the dream and a dreamer. The first case, if applied to us, gives us this: if we are nothing but a dream, then we are our own reality since there is nothing else. Our dreams would be dreams, but as for us ourselves, we are the reality and our "plane" is reality since there is nothing else but what comes from us.
The second case, if we are nothing but the dream of some god or alien, reduces to the first case. We (well, I at least) know nothing of the dreamer who has dreamt me, so while his reality may be the foundation of reality, only the stuff in my "plane" is of my reality, since nothing exists for me outside of the dream. That is to say, if I am being dreamt, I cannot leave the dream and enter the reality of my dreamer, for instance. Perhaps the dreamer may enter his dream, but then he is merely a part of his dream and not some other thing. Even if the dreamer were to bring with him something that had formerly not existed within the dream, it would then simply become a part of the reality of the dream. So if we are the dream of some other being, our reality is still our reality.
What it boils down to is this: Is it
technically possible that we are only the dream of some alien or god? Well, the argument above doesn't actually refute that. What it says, is that we are real relative to ourselves. Since we know of no one below us dreaming us up, then it really
doesn't matter at all that we are only a dream since we are surrounded with our own reality.
Go ahead and pick this apart if you like.
None.