The phrase dream about/of is translated as Soñar con in Spanish.
If I literally wanted someone to dream with me (and not dream about me), how would I say that? For example, a character in the movie Inception might ask another person to dream with them, and they mean "join me in a shared dream" and would definitely not be asking the other person to dream about them.
Would it be enough to just add the word junto: sueña junto conmigo?
I realize this is kind of a contrived question, so sorry.
The question is indeed contrived, because the situation in question is only possible in fiction (so far) and therefore common language is not really prepared to express it. Prepositions are often arbitrary and it's just a coincidence that in Spanish the phrase goes soñar con….
You can let context do its job and just use Sueña conmigo. Or you can say more explicitly Sueña junto conmigo, which sounds a bit off and has no poetry or sense of intimacy in it. Or maybe you could paraphrase a bit and say:
The former has a good precedent (it sounds like a slogan or a song title, which it is, actually). The latter resolves the ambiguity of the meaning of con by placing the preposition next to a different verb.
My answer will be short.
The one that sounds more natural to me is
Sueña conmigo
But it is right that it can also be understood as "dream about me", but the context would make the rest. If, anyways, you want to explicitly make the difference, what I'd say is
Sueña junto a mí.
Which is the closest way that doesn't sound bad to me, and it means the same. What's more, I think I've heard it in some children movies. For me it definitely sounds much better than "sueña junto conmigo".
I can imagine someone saying this without any fantasy/science fiction. It's a romantic idea. After all, soñar | dream isn't just about what we do when we're asleep. Here's one way that occurs to me to express your idea:
Ven a estar a mi lado en mi sueño. Or Acompáñame en mi sueño.
Now let's go a little farther with it. Let's say that A says to their partner, "Last night I dreamed that I half woke up from a beautiful dream, and took your hand to take you back into my dream with me. Let's try it tonight! Let's see if it works!"
Anoche soñé que me medio desperté de un sueño muy bello, y te agarré de la mano para llevarte conmigo a mi sueño otra vez. Vamos a probarlo etc.
Although I don't agree with Pablo about the idea being too contrived to come up in natural conversation, I do agree that in the right context, "Sueña conmigo" could work.
Note about my quasi-translation: I tend to take a gestalt approach to converting an idea from one language to the other. I think about the idea behind the original sentence and then let it express itself in the other language. So my results might be pretty different from what one would get from a strict translation as such. So, I'm not sure whether my answer is quite what you were after....
