Despite Salvia bad reputation and even my own fear of it, it is not all darkness. It shows the most profound and uncomfortable state of consciousness that it often shocks people and due to ego death there is very little one can do to prepare for it.
Salvia is a teacher and lessons are not always pleasant. Salvia shows you the raw reality of your own state of mind.
Only thing to fear is you.
I'm actually not entirely sure that salvia can cause ego death...it actually seems that's the only thing that actually remains most of the time while everything else dissolves (memory/knowledge/etc., but "I" am still experiencing this experience). I think I also understand what you have experienced though, but I just think there needs to be a different name for this because it is fundamentally different than ego death experienced on traditional psychedelics (your entire sense of self goes away too...there is no more "you" at all).
From personal experience... With salvia, "I" still exist and "I" have a hell of a time. But with ego death induced by psilocybin, there was no more difference between the universe and myself, and "I" was simply no longer a thing anymore. It's almost like salvia is the exact opposite in that it's a sort of hyper-focus on the ego rather than the death of it.