Author's Note: Something about Amy remembering everything back to existence in the Series 5 finale reminded me of poor Donna, never able to remember her own time with the Doctor. So here's my Donna-inspired tid-bit. She is, after all, my favorite companion. Enjoy!
Donna wakes up crying sometimes.
She comes to with a gasp and a profound sense of loss, and on those nights when she wakes up crying it's from dreams. Dreams about someone that meant nearly everything to her.
Sometimes, Donna can remember bits and pieces of the dreams. She can remember a man who talks a lot, and really sees her potential instead of brushing her off. He takes her seriously. In those dreams, they have the best of times together, even though Donna can't remember what they do. In some dreams they just talk, but each conversation has meaning.
When she wakes up Donna tries to remember the dreams and why she has tears on her cheeks, but everything slips from her memory like sand through her fingers, and she's only left with that feeling afterwards.
She feels like somebody's died.
One night she writes down "Remember" on a blank sheet of paper and keeps the thought with her as she falls asleep, but the dreams slip away same as ever.
Some days she finds herself tearing up at the strangest things. A phone rings, and she starts crying. On one occasion Wilf takes her up the hill and points at the stars and she can't help it, she ends up sobbing and telling him all about the person she's felt she's lost and he tries to help her, really, but he can't. He tells her so and Donna believes him because he's always helped her in the past, and if he says it's out of his hands then it must be.
She wonders, despite herself, if her mother and grandfather know something she doesn't. Especially her mother, who's been easier on her these past few months. Almost as if someone's died and they're trying to make up for it. There's that thought, again.
Between the feelings of loss and the dreams life returns to normal, except there's always the questions lingering in Donna's head. What's missing? What's different? What's changed?
In an ideal world Donna knows she would see these things that make her upset and suddenly be able to remember everything that triggered it, and she would be, if not happy, at least fulfilled in her knowledge. Or perhaps the dreams themselves would tell her what she lost, and she would remember from them.
Nothing like that happens. Donna does not remember. She only knows the dreams and the feeling she gets every once in awhile that makes her feel like she's lost the universe.