U Ba Fin:
@Chuck - I just reread Ingram’s description of first and second Jhana in MCTB and totally see what you mean. The description is very similar to what I articulated above. May well be a Jhana.
I went through the MCTB definitions of Jhanas 1 and 2 for comparison. For the first Jhana it is stated that
As concentration improves, it is as though the mind “sees” the first
jhana and grabs on to it. Having an idea of what you are looking for, i.e.
something enjoyable and steady, can be helpful for this. It has the five
primary factors of applied and sustained effort or attention, rapture,
happiness and concentration. Thus, it is great fun, feels good, but takes
consistent effort to sustain. The attention is focused narrowly, as though
one were looking at a small area of this page. This state can be quite a
relief from the pain and discomfort of sitting meditation and can
temporarily quiet the mind somewhat. As with all the concentration
states, it is generally quite easy to concentrate on something that is very
enjoyable. Thus, one’s concentration skills may improve rapidly and
easily after attaining the first jhana and tend to basically flounder until
one has attained the first jhana. Thus, attaining the first jhana is really,
really important.
In my experience of this "space in my mind" there is not the quality of applied of sustained attention of any effort. The thing happens on its own when I drop as much doing as I can. Also I woudn't call it rapturous or happy, but these are more debatable since there is this cool, equanomous, wonderful aspect that feels more like loving deeply.
The second Jhana chapter begins with this:
The second jhana is like the first, i.e. a seemingly solidified mind
state. With the dropping of almost all of applied and sustained effort the
rapture and happiness factors created by concentration can really
predominate. Thus, whereas the first jhana feels like something you
need to pay attention to, the second jhana has the quality of showing
itself to you. The focus of attention widens out somewhat, sort of like
looking straight ahead without focusing the eyes on anything specific.
Whereas mind-generated objects in the first jhana are stable, they will
move (e.g. spin, pulse, resonate, etc.) in the second jhana in ways that
correlate with the phase of the breath, moving slowly towards the top
and bottom of the breath and more quickly in the middle.
So here the effort is dropped almost completely. I still don't see the happiness and rapture predominating. And also, there is nothing moving/changing with the breath. There is this stability in what I experience.
Now third Jhana looks more like it:
In this state, the rapture drops away, and what is left is more cool
“bodily” bliss and equanimity with a lot of mindfulness of what is going
on.
.
.
The attention is now in wide focus, sort of like resting in the half of
space that is in front of one’s self.The third jhana is like the
counterpoint to the focus of attention of the second jhana. In the second
jhana, wherever we look we see clearly, whereas in the third jhana the
wide periphery of our attention is clear and the center of our attention is
murky. This can be extremely confusing until one gets used to it, and
trying to stay with one object in the center in the third jhana will cause
the meditator to miss what this state has to offer and teach. Moving from
the second to the third jhana is like going from focusing on the donut
hole to focusing on the outer edge of the donut, except that now you are
sitting in the center of the donut.
.
.
In its pure and simple spaciousness, profound clarity, balance and
contentment, the third jhana is even better than the second jhana.
Simple spaciousness, clarity, contentment sound like what I have. I'm not so sure about the central vs periphery attention though. It's more like both are present equally.
Oh look, the fourth sounds even more like what I have

As before, if the student wishes to go on to the fourth jhana, then
they just cultivate the third jhana and begin to pay attention to the fact
that even the bodily bliss is somewhat irritating or noisy. Eventually, the
mind will abandon the third jhana and shift into the fourth jhana, which
is the height of equanimity. This state is remarkable in its simple
spaciousness and acceptance. The extreme level of imperturbability
would be astounding if there was not such pronounced imperturbability.
This is by far the most restful of the first four jhanas.
The focus of attention is now largely panoramic and thus even
saying “focus” here is a bit problematic.
I stop with the quotes now, but I read through all the jahanas and they seem to resemble more and more what I'm having. However. I'm not doing concentration practises, as this state of mind tends to arise fairly quickly and with the guideline of "doing nothing" or "dropping all doing"so it is unclear to what extent these definition of Jhana should apply. Also, I meditate with my eyes open. So, it is a different animal than these Jhanas, although it has certainly been useful to read about these after a long time. I notice how much my practise has advanced since I can now relate to these desciptions instead of reading about them in awe!
Still, I'm not sure what I have. I'll keep meditaing and calling it a natural state :]