For all intents & purposes, SI = fear of death
Fear of dying seems more fitting. Death is only an idea, one that we don't understand at all, one that might be understood as the opposite of being, but, if we percieve being as a kind of constant dying, as many of us do, death might be understood as the opposite of dying. Then we may find comfort in the idea of not being, because we see it as the resolution of the dying process.
In the same line of thought, extended further, that logic brings us the fear of surviving, of not achieving resolution, of prolonged dying in a future that might be even more painful.
Because the cost of dying - that we know. We know what dying entails. It's not just irrational fear playing tricks with our imagination, it's the experience of being ripped apart piece by piece and still breathing, speaking, posing the question - how much do we have to suffer to actually make this living body drew its last breath? And if we fail, what terrifying and hellish form will dying assume?