There are two basic kinds of awareness available to the human. One depends on the other, but the “other” is rarely experienced, as it takes deliberate effort and training to experience it. The rarest of individuals have the ability to constantly maintain both the usual “normal” state of awareness, and nirvanic awareness as a simuiltaneous and complete integrated state of perception. “Daily” awareness, the one that most humans never get past, is called by those who have, “subject-object awareness,” is what constitutes what we call “me” or “myself,” and is mistakenly refered to as “I.” The nirvanic phase of awareness is a wakeful state with no contents of referent save for Meaning and Substance, and feels like Bliss. It is yet not the “highest” state attainable, but is the doorway. It may also be, in my opinion, the door to the inspirations and insights given to musicians, artists, writers, inventors, anyone with a creative inclination.
A common mistake of exegesis regarding this state for those not trained to hold it as an experince is to think it is a temporary occurance. In fact, it is, as stated above, the substrate of ordinary daily awareness, but is clouded, as “through a glass, darkly.” A firm understanding of this state has certain implicatons for the ordinary christianist view, though, because even statistically there are a number who naturally experience it, some christianists do get through their belief system and are able to arrive at a useful and practical understanding of the state and its implications. This is rare, but it may be sort of what St Theresa experienced with certain psychic and mystic modifications. But it is, in my opinion, quite likely what St Thomas Aquinas experienced when he stated after his greatest revalations that all his writings “are as straw.”
This is due to the difference in mode of experience that such a revelation is founded in. Our ordinary every day faith is exoteric, depending on the acceptance of a way of belief and the rational that supports it. Having a nirvanic experience puts the relationship of the experiencer no longer on faith, but on a kind of knowledge called “knowledge by identitiy.”
A very good treasties and fuller explanation of all this is found in the works of Franklin Merrell-Wolff. His two pubilc works are Pathways Through to Space, which is a diary of his transfomation in awareness, and The Philosophy of Consciousness Without an Object. They are written originally in English, so there is no need to learn a whole system of Eastern thought just to even intellectually “get it.” The second work, diferent from the more casual nature of the first, is somewhat abstruse, it being a more methodical and a very self-critical exegesis of the experience and its necessary meaning. But it is very clear about the nature of nirvana, and would be an excellent and complete answer to your question from someone who has “been there.”
For lighter reading, I might suggest *A Thousand Names for Joy *by Byron Katie, whom I consider to be a person stabilized in the balanced state. Her book is a delightful read, very uplifting, and an window on the perceptual patterns of someone who is in that fortunate state of awarness. For a question and answer type of read, there are several such, both of Western and Eastern origin.