Hari Om !
Well, this is a question....I still have not found a complete answer. I am still searching. Whatever I have understood till now from the teachings of Swami Sivanandaji and Swami Chidanandaji, I would like to present. Enlightenment or God realization or God consciousness is really a state of being. Maybe a mental state, but I am not so sure since it is believed that there is no mind when there is enlightenment.
Basically, human beings exists with a 'world consciousness' state, which would mean that human beings give utmost importance to themselves. Their self or the 'I' dominates every action of theirs.They think they are responsible for everything that is happening.....success, pleasures, pain, sorrow, etc. The level of attribution does varies amongst human beings. When one transcends from 'world consciousness' state to 'God consciouness' state, the self or the 'I' factor disappears. They would start believing that nothing is due to themselves or the 'I' factor. They believe everything is happening because of God.....hence everything is attributed to God.....good, bad, success, failures, sorrow, pain belongs to God. They feel that they are mere instruments in the hands of God.

As one transcends from the 'world consciousness' state to 'God consciousness' state, they start believing that God who is formless,nameless, timeless, endless, etc is everywhere. They believe that their own self (atman) or soul is nothing but a part of God. They identify themselves as same as God. Perhaps, this is what the great philosopher
Sri Adi Sankaracharya consolidated in his
Advaita Vedanta , and the
Upanishads imbibe constantly as "Aham Brahmasmi (I am Brahman)" and "Tat Tvam Asi(Thou art That)". As one grows in spiritual consciousness, they identify themselves with everything in this world. They become extremely compassionate to every living being and even to non living being. Even though they live in this world, they are not attached to the 'worldly things'. They are in constant remembrance of God.
Om Namoh Bhagavathe Sivanandaya !
Om Namoh Bhagavathe Chidanandaya !