An image of a twinned pregnancy (in this case, of 2 co-twins in utero) at about 10 weeks. The lower sac contains a live fetus, but the fetus in the upper sac has died. This is the simplest example of how loss in pregnancy can result in the birth of a 'womb twin'.
The surviving co-twin in the above pregnancy will carry an imprint of that very early loss which will exert a lifelong effect on them. It may not be conscious and may not always be problematic. But the effects often are felt to be challenging, throughout one's life. The sense of Something or Someone being there for a while but now gone missing can remain somewhere in the back of the mind of the survivor - the 'womb twin survivor' - and this can be at the root of various subtle (some less subtle) patterns in daily life.
The above scan is just a simple example of how a womb twin can come to be born. There are other ways, as we described here. For example, a scan might reveal a twin pregnancy that continues, with a third embryo that has died. In this instance, even though the survivors would be born as a live born twin pair, each of them would also be a 'womb twin' as they each lost a co-twin in utero.
This research project, started by Althea Hayton in 2003, is the first project of its kind to explore in depth the
psychological impact on a surviving co-twin of the loss of one or more co-twins during pregnancy or close to birth.
It might seem impossible to explain how such an early event could leave an impression - but much research supports the idea.
So, if you have always had a sense of 'being a twin', it is quite possible that you are right. Above all, you are not crazy!