What does it mean when you have the same dream over and over?

My dream is about my dog who passed away last year. I keep replaying the last night the night he was put to sleep :(. It changes sometimes because I sometimes see him just laying on a table struggling to breath and Hooked up to a lot of i.v.s. Sometimes it ends with the vets loosing is cremated remains and I go insane. I just don't get why I keep having this horrible replay ad not good memories of him. I have been having these dreams for almost a month straight maybe linger and always wake up in tears! What does this mean? What are some ways to help sleep cuz now I'm to the point that I'm afraid to sleep!!!