So, when a person enters nyamnyid and/or lhundrub, does the pain typically associated with getting hit by a brick cease? Is this due the dissolution between subject and object, realizing that the energy of getting hit by a brick is the same sort of energy as having sex, etc.?
I'd say don't even try to form an idea of what any aspect of fruition would be like. Holding the expectation negates abiding in the base and is actually a projection of mind. See that an expectation of a 'future' event (or state) is just a presently arising thought, and the presently arising thought is merely an empty play of the primordial nature. Which as Namdrol was pointing out above, seems to arise, seems to abide, and seems to fall... but does it? Be here now. The base is ever-present.
But for the sake of conventional conversation; upon the dissolution of duality, the qualities(characteristics/properties) which constitute a brick or pain would be empty expressions of the primordial nature. Putting it into words becomes clumsy because one has to use descriptive language which conveys elements of experience which are absent in the base. Even now, our language actually conveys elements which are not present in experience. Alan Watts gives the example of the famous 'it' in "it is raining"... what is this 'it'? It's just a convention of language. All language is like that, it populates experience with 'things' which are not evident when investigated empirically. Some are harmless, like the 'it' in 'it is raining' and some are very powerful and become engrained subconsciously like 'you' and 'me'.
So for this reason a nondual experience cannot be described accurately at all. But to ignore that fact for a moment, and attempt to frame an answer to your question in a clumsy way which ultimately misrepresents the actuality of what it would be like: you would BE the pain, and the pain would be a play of your nature, but 'you' would be absent so the pain would appear to itself and any notion of it being an unpleasant or pleasant experience would not arise. I mean, we can't even comprehend how profound a state that is at that point. That's why you read all these stories of miracles and 'powers' because the constructs of space and time, subject and object are no more. But THE MOST IMPORTANT THING is; do not strive for that, don't want or wish for that, don't expect that, in practice if miraculous experiences such as visions or experiences of nonduality arise view them with an attitude of indifference... do not care, never think you have achieved anything. Know that all is a play of the primordial nature, reflection on the mirror, if something miraculous arises and there's an inkling of achievement correct for that immediately and remain unmoved. Just remain in the base and there will be no limit to your practice. Don't postulate any kind of notions about what the culmination of effort would be like, because it's coming from the perspective of ignorance(avidya). Humility and earnestness are of utmost importance.
*All this is my unfounded opinion