your feeling 'I Am' (I exist)
your spirit and soul
The Self is existence, realized, not experienced, a non-spatial spiritual reality. Existence imagining experiences. The feeling 'I am', awareness, spirit, consciousness without space. Birthless, Self existent, immortal. Christos (Christ-consciousness), Allah, the Tao, Buddha Mind, Wahe Guru, Atma, Paramatama, Brahman, One Mind, Ein-Sof, etc, are all different labels for the Self.
Subject subtler than observing instrument, quest futile. Consciousness more subtle than mind, employing mind to realize consciousness is futile. Only one's consciousness can be conscious of (realize) consciousness. The only thing you can be truly sure of is that you are conscious, a 'subjective truth' you can neither deny nor ever prove to anyone 'else'. Mystics conclude birthless existence is a mystery, perhaps even unto it Self. Soul truth (atma vidya) purifies mind (thins out conditioning) so in quiesence you 'realize' your true immortal Self.