What does it mean when, in your dreams, you get what you've always wanted, but then it gets taken away from you?

I have this dream, that turns into a nightmare. Its so incredibly surreal, and vivid that I remember it for so long afterwards. I end up crying, screaming and yelling in my sleep.. So. In reality, I would LOVE to have a kid. But Im not so stupid to go out and do it, I know Im gonna wait lol. The dream is the same every time, only a bit longer too. And in this dream, I have an adorable baby girl, her nickname is Sunny. Shes pretty young, yet in this dream her voice overpowers all others. Im guessing shes only about 2-4 months old. I carry her in my arms the entire time. Im still the same age, same person. I dont know why her nickname is Sunny.. I have friends and family walking around me at all times, which I think symbolizes my support at first..But then I notice how they are on edge all the time, as if they were trying to protect Sunny like something was after her. We walk around a park, laughing and talking, everything is going wonderfully. I kiss her on the head and tell her how much I love her. Right afterwards I reach the fountain and look down..it was only maybe 2 seconds later. I look down, and Sunnys gone. Slipped right from my hand. I can hear her startled cries, and whimpers fading away..I run after her. I run. And run, and run. I can hear her little voice screaming tears, trembling with every footstep. I search for her, getting closer and closer but never to even touch her ever again. These things that took her, they were hooded in black from head to toe, with crooked smiles, pale skin and black mouths. In the dream I always get close to finding her, but can never get there. Once, I could almost reach out and grab her from the things arms, but he threw these wierd pieces on the floor that made it so I couldnt get past it, like a barrier. I stood there. Facing my child in its arms, while it smiled and laughed at me. My babys cries are louder than ever, and I cant stand it. Once my first tear fell, they disappeared and I ran after again. The entire time, I could hear Sunnys cries in my head like a giant headache, pounding and throbbing worse than ever. I wake up with a scream, jolted away from my dream while trying to find her. I have that headache for the rest of my day. Sorry for how long this ended up being lol. I could write a book on it lol its such a long dream. Whats it mean, do you think? I know it means something. I have it often..worse every time, longer every time.