An important distinction is that a boltzman brain only "works" for an instant before the harsh environment of space destroys it. There's simply no time for a whole dream matrix reality to play out.
Another Boltzmann brain can pop up, which contains a short term memory of being previous Boltzmann brain. Sensory inputs aren't constrained though. Most probable sequence of such brains should feel like noise all over your senses, I think.
Why? The time passed for the Boltzmann Brain won’t necessarily be tied to its real frame of existence i think, it may simulate any timeframe imaginable, depending on its starting conditions.
In fact the simulation of any timeframe would be constrained by physical laws.
For example for a Boltzmann Brain with a similar chemical composition as ours the speed at which chemical reactions occur would limit the speed of experience.
For a Boltzmann Brain that simulates ours with a very different physical substrate the speed of light would still be a limit.
