Seinsvergessenheit is usually understood to mean the forgottenness or oblivion of being.

Seinsvergessenheit is also an electronica goth band.

Sometimes Heidegger uses Seynsvergessenheit.

Not to be confused with, Seinsverlassenheit which is the abandonment, of beings, by being. In the Contributions to Philosophy, Heidegger says it distresses him, and differenciates his ontology from that of Aristotle's epoch; i.e. from Anaximander to Nietzsche.

[The grounding question] is not the continuation of the version of the guiding question in Aristotle. For it arises immediately from the necessity of the distress of the abandonment by being, that occurrence which is essentially also conditioned by the history of the guiding question and its misconstrual.
P. 165

Note that in the translation they appear to have confused Seinsverlassenheit with Seinsvergessenheit because the book has abandonment of being, but I've corrected it. But they both apply. The guiding question is of the being of beings; the question of metaphysics. The grounding question is of the openness of beyng. What is both forgotten and abandoned is enowning. Except right here, of course.

Heidegger's distress is from our lack of distress.

The lack of distress is the greatest where self-certainty has become unsurpassable, where everything is held to be calculable and, above all, where it is decided, without a preceding question, who we are and what we are to do -- where knowing awareness has been lost without its ever actually having been established that the actual self-being happens by way of a grounding-beyond-oneself, which requires the grounding of the grounding-space and its time. This, in turn, requires knowing what is ownmost to truth as what knowing cannot avoid.

But wherever "truth" is long since no longer a question and even the attempt at such a question is already rejected as a disturbance and an irrelevant brooding, there the distress of abandonment of/by being has no time-space at all.
P. 87

Distressed, or not; questioned, or not; the abandonment of, or by--it is always the same--beyng.  ¶ 10:37 PM