Sartre's work in ontology, which is an attempt to categorize Being and Nothing adequately, claims that being is transphenomenal or irreducible and is distinct from phenomenal objects creating a duality, not of mind and body like Decartes who explores the division between the mental and material, but a phenomenological dualism such that both categories are primarily mental. He speaks of an intuition of the phenomenon of being and does not believe that it is a composition of being of phenomena. Unlike phenomena which might be reduced to knowledge, being is itself a sort of dynamic process related to the growth of human reality which occurs along three dimensions: being-for-itself (nothingness), being-in-itself (the inert givens of our experience), and being-for-others (our social experience). These three dimensions of beings highlight the three categories you mention: pre-reflection, reflection, and self-reflection.
Going from nothingness to being is a phenomenological perspective that the Self begins to realize itself by transitioning from being-for-itself to being-in-itself, whereby the former nihlates the latter, particularly by the recognition that the negatives are not merely the lack of phenomena, but are actually phenomena in themselves, particilarly absence, distance, regret, or lacking. It is this transition from pre-reflection, where consciouness is primarily oblivious to the Self, that the one becomes reflective. But, then one eventually is forced to grapple with the Other, which is an ontological claim regarding differentiating intentionality of the Self from other minds.
This increasing distance from the conscious mind from itself is what characterizes human reality, which is the non-reducible, non-synthesizable duality between Being and Nothingness. The distance gives rise to temporality in the past, present, and future, temporal existence allows for ontological freedom because the self becomes the presence to self, and lastly, the distance creates the paradox that reality is what it is not, and facticity is subjective, because the nature of self-reflection as imaginative is ultimately seizing the power to recreate oneself, to choose Being. This ability to choose ultimately leads to existential dread.
Is self-consciousness self-thetic? In so much as that the Self, which is authentic rejects dogmatism, rejects the inert, and embraces the freedom to self-author. It is also includes the act of recognizing the pre-reflective cogito, since cogito, or linguistic proposition, does not fully describe the Self. The idea of the authentic self fully embraces the terror of existential freedom which necessarily involves choice and responsibility. Later on Sartre characterized self-reflection more thoroughly and extended his position somewhat from his ontology in Being and Nothingness to existentialism, Marxism, and ethics, such as Existentialism and Human Emotions, Search for a Method, and Critique of Dialectical Reason.
