Comment by NobodyNada

A dream is a totally incoherent result of random fluctuations, but it seems real and coherent until you wake up. A Boltzmann brain only exists for a very short period of time — on that small of a timescale, your existence is really just a single instantaneous snapshot of a state of mind, and there’s no time to recall a sequence of memories or think through logical propositions. Even though existence feels coherent, that feeling would be just a false memory.