Without being able to question you personally in order to gain more clarification about the description provided, and going
only on the description given, I'm inclined to agree with Tommy.
Jane Laurel Carrington:
I seem to have made some sort of breakthrough on a recent daylong retreat. I've been doing samatha practice exclusively for a couple of months without much success, focusing on the anapana spot.
What is the "anapana spot"? In your estimation, that is. I've never heard this term used before.
Jane Laurel Carrington:
Lately I'd been going into a twilight state where bits of dream imagery come and go; I thought I was sleepy, but then I'd lie down and not go to sleep, so I wasn't sure.
This sounds very much like a dull minded kind of state that is very common with beginners attempting to achieve jhana (and even those who may not be attempting to achieve anything at all, but who are just going with the flow of events during meditation). When I say "dull minded" I'm referring to it being "without sati" or mindfulness. This state could very well be described as "dreamy" in texture as it reminds practitioners of that dream-like, very pleasant state of consciousness that occurs just prior to sleep when the mind relaxes and is about to become enveloped in sleep. This can be a very suggestible state to maintain, which is not good, meaning the mind can become open to the power of suggestion as in an hypnotic state. This semi-hypnotic state is
not a state that you want to cultivate. The reason for the lack of alertness and sharpness in the experience stems from the lack of mindfulness when entering it. In order to avoid this semi-hypnotic state, maintain your mindfulness when attempting to return to this relaxed, at ease state which might be described as being jhana.
Jane Laurel Carrington:
Then what happened on the retreat as I was sitting in this dreamy state is I suddenly felt a sense of clarity snap into place in the breath going in and out over the anapana spot, and all the dream stuff ceased.
Now, this sounds like your mindfulness kicked in. And that's a good thing. Because it presents the sharpness, alertness, and clarity that you want to cultivate in the effort to strengthen overall concentration. It is from this state that insight contemplation can take place and can have its greatest impact on your awareness and conscious realization.
Jane Laurel Carrington:
I haven't been able to get this back since returning to daily life; am hoping to get it back in a long weekend retreat coming up. But I am wondering what it was that I experienced. It definitely felt different from anything I've had happen before.
That's a very common experience, that is, feeling as though you have difficulty reconstituting the experience. You just have to relax (somewhat) and let it occur for it to re-occur. Once you figure out how to do this
at will (so to speak), you will have figured out how to enter it whenever you wish without much effort in doing so. And once you are able to do that, you should be able to also maintain mindfulness at will (although this might take a while to fully develop). And that is a good thing to cultivate. Because it allows you to "see things as they are" rather than how the conditioned mind might erroneously perceive them to be.