As an in-utero-twinless twin I don't have the "usual" memories of my twin. I don't remember her face, her laugh, what we did as kids, our birthday parties, pranks we played on people and so on.
My conscious mind, the part of my brain that holds pictures, sounds and events, goes blank when I type in "twin".
Other parts of my brain don't. They do remember, but it's not so easy to find them. They're burried under the conscious stuff like a hidden program in my computer running in the background all the time and taking up much MUCH working space, but visible only if you know which keys to press.
Most data there is about the loss, about panic and fear, abandonement, negative feelings. It pops up first, but when I dig deeper and try to reconstruct older files, I find more.
I find a memory of entangled limbs. Of feet and legs touching and floating apart. I find a lot of floating and touching, actually.
It runs in the back of my mind, where consciousness never goes, because it's to primarily and messy for the educated mind (hrrm!). It pops up and vanishes again, it can't be printed or converted into a JPG-file...
BUT IT IS THERE! IT IS REAL! IT'S MY TWIN!