If you're meditating, how do you know that you're meditating without having, at minimum, a working short-term memory? If meditating actually disabled your memory, wouldn't you immediately forget that you were meditating and stop?
All I can say is, try meditating sometime and you will see. (I don't recommend mantra meditation, but rather something more like Vipassana or "mindfulness" or any meditation that is not about distracting your mind by keeping it busy).
When you become comfortable with meditation, you become very aware of what your consciousness is doing. You gain a palpable sense for the present moment. Once you have that, it makes a lot of these kinds of questions unnecessary (or at least the questions become very different in nature). If you don't have this taste for the present, then asking/answering questions like this is like trying to explain colors to a blind person. It just doesn't work because most of the questions are about things that don't really have anything to do with consciousness.
> the point is that unconscious processes can be explained without hypothesizing consciousness
This really doesn't make any sense, by the way.
To borrow Metzinger et al.'s terminology, this internal model of what consciousness is may not be very transparent to us (much in the same way why we don't have good intuitions why/how it is that we have notions about solidity and classical (in one or other sense) mechanics (it is useful to have an image of a solid tree/obstacle when running through a forest while being chased by a tiger, and all that.) We may have some intuitions, but those intuitions may turn out to be wrong.)
: A very interesting book I'm yet to read: http://mitpress.mit.edu/books/being-no-one
Working memory can hold a limited number of things (usually said to be 7), whereas short-term memory has a larger limit in capacity and time. These are both temporary systems that feed off each other and rely on the larger long-term memory to give meaning and context to the "symbols" they contain.
Everything is interconnected, so making definitive statements about any of this is hard.
(IANANeuroScientist but my work does Neuroscience research)
So, are such states hallucination? Every person (human being) knows for sure that they are real.
I believe meditation is pulling focus into the present moment, but I also believe that moment is far from discrete.
Ultimately, the idea is that the state of 'here-now' (whether arrived through practice, observation or heck even induced through means of substance - though there are differences) is the state when You are not your mind anymore. So in that sense, looking at above suggestion about memory, I would simply ask: what is the need of a memory?
(It's terrifying what your brain does in sleep....)