Think of yourself not as confined to a small body, but think of yourself as, in your natural state, being expansive and the size of the universe. You are omnipresent, you are everywhere and in all things. You share the entirety of existence with all other children of God. You overlap with everyone. You exist in the same space, share all of your being with other beings, and commune intimately in a state of oneness.
What happened to that self, which was a universe-sized fully sharing being, in the separation idea, is you attempted to withdraw from immersion in the whole, you confined yourself, you shrunk down, you limited yourself, you withdrew yourself from the communal experience, and so made yourself show up as an isolated body person.
You became small and little and weak and frail, fenced off from the rest, not wanting to share with anyone, wanting to have something special just to yourself, something exclusive, something that only you have, which makes you different and unique and selfish. Instead of being everywhere you decided to be somewhere, restricted in spacetime to a small tiny spot, around which you defend against the entire universe from entering.
This is what happened in the separation. This is how you took your pre-existing sharing self, and "made it separate". You separated it from its communal experience with other infinite beings, putting yourself in a corner and walling yourself in, in order to keep them out and you in. You did not want to share in them, and you didn't not want them to share in you. This was the purpose of the body idea, a separation device and a wall of flesh around the mind.
This produced what is termed "the separated self" which is a self who used to share with everyone, who now does not want to share at all. This imprisoned self, is still a real self, but has placed itself under limitations. And these limitations are made of illusions, which seem to now substitute for a sense of real, full self, making it seem as though you "made up a self" to replace the fullness of your soul. You made the body, and identified with and as it, in an attempt to isolate and exclude. This is all that happened in the separation. You just became selfish and special and different.
The restoration of your true nature simple entails the willingness to drop the walls, remove the isolation, transcend the body separation device, return to being the size of the universe, re-immerse yourself in creation, rejoin the community of the Sonship, and resume a state of perfectly unselfish sharing. The willingness to let others share you, as much as you share them. Restored to being your natural self as God created you, a self who is equal to all real brothers and who shares everything with everyone.
Once you can see what you were like BEFORE the separation - a limitless universal being who shares everything with every other limitless universal being - the family of God - you can easily contrast this against the position you now find yourself in, and realize that it was the attempt not to share that put yourself into this situation. Where you are now inside a body, everyone else is kept outside, you seem to inhabit it alone, and now no-one shares anything with you inside your little fence. Being kept apart and separated off and unwilling to join, is a lonely and isolating experience.
The walls of separation, the body itself, all physical matter, all illusions, the ego, body identification, forms, the world, all things little, every prison wall which keeps you from sharing and immersing yourself in communion with God and Sonship, which occurs only in Heaven, keeps you from being IN heaven, and keeps you imprisoned. This is why the body cannot contain you who are love, any more than God can enter a body or join you there. You must expand. You must become unlimited. You must return to being an eternal being who is everywhere and sharing with all other eternal beings in an unlimited, open and unselfish way.
"The ego is the idea of selfishness. The soul is the idea of self-fullness."