If you meant the phrase, "in your dreams" (as in the reply one would give to an overly optimistic idea or thought), you can probably go with "別做白日夢了". If not, the answers above are perfectly fine .

在你＂的＂梦里 sounds so strange. maybe 在你梦里 or 你梦里 is better. 用那么多虚词抓子嘛= =！

在你的梦里

在梦中

"在你的梦里" zai4 ni3 de meng4 li3