One of the main goals of Hinduism is to attain god-realization.
How does one know he/she is in that state? What changes?
Are there any Hindu texts that provide details on what that god-realized state feels like?
Such questions can only be answered by the one who has tasted divine bliss and fortunately the same question was asked to Sri Ramakrishna Paramahamsa by one of his devotee.
Gospel of Sri Ramakrishna / Volume 1 / The Master's Birthday Celebration at Dakshineswar
AMRITA: "Sir, how do you feel in samadhi?"
MASTER (Sri Ramakrishna): "You may have heard that the cockroach, by intently meditating on the brahmara, is transformed into a brahmara. Do you know how I feel then? I feel like a fish released from a pot into the water of the Ganges."
AMRITA: "Don't you feel at that time even a trace of ego?"
MASTER: "Yes, generally a little of it remains. However hard you may rub a grain of gold against a grindstone, still a bit of it always remains. Or again, take the case of a big fire; the ego is like one of its sparks. In samadhi I lose outer consciousness completely; but God generally keeps a little trace of ego in me for the enjoyment of divine communion. Enjoyment is possible only when 'I' and 'you' remain.
"Again, sometimes God effaces even that trace of 'I'. Then one experiences jada samadhi or nirvikalpa samadhi. That experience cannot be described. A salt doll went to measure the depth of the ocean, but before it had gone far into the water it melted away. It became entirely one with the water of the ocean. Then who was to come back and tell the ocean's depth?"