What does 'awareness of the flow' mean

Awareness of the flow is surrendering your mind to a higher truth, being centered on your non-being beyond the material plane, and observing the outwards events flowing like clouds. You are fully aware of the passing clouds, but you're not caught in the drama and are not affected by it.

I like to suggest the book Models of Brain and Mind: Physical, Computational and Psychological Approaches page 249 and onwards.

There you can find Awareness of sensation, mind or consciousness, mental contents. The four domains of Satipatthana

The awareness flow in Vipassana

For a practitioner of Satipatthana, one should have prerequisites before doing any Satipatthana, then one should sit in quiet place and do practices of Awareness of body (Breath or Kaya Cinkhara). After enough of practicing Awareness of body, the practitioner can have strong concentration to continue Awareness of mind or consciousness(Citta Cinkhara). This is recommended practice because Breath is comparatively slower in sequence than mind or consciousness. Any practitioner without properly trained Satipatthana of Awareness of body cannot practice Awareness of mind.

Awareness of flow is process in Awareness of mind or consciousness. The essential part of awareness of flow is the practitioner must not stimulate or initiate any feeling or thought. It is crucial the awareness (Sati) must be quick enough to catch up when there is any change of the state of mind/consciousness. Train of thought, feeling or sensation is not allowed to happen because it is required the effort or attempt to make this happen. At least, when feeling or sensation is happened awareness is quickly followed and the feeling or sensation is ceased to continue to be mature to train of thoughts. By mastering this technique, awareness of flow is obvious in practitioner's mind. Any state of change of mind can come and go and awareness is always in between of the flow. The result is mind is clear and free from craving, anger and other hindrances that make one's mind to pollute.

The above explanation is very succinct note and details studies of Satipatthana is required to practice it in real world and it'd better join long retreat to Vipassana meditation center to seek correct guidance to do so. The below references are recommended details of Satipatthana and you are free to adopt any practice preferred or comfortable for you.

References

1. Satipatthana Sutta Audio
2. Mahasatipatthana Sutta
3. Practical Vipassana Exercises

"Awareness of the flow" doesn't seem to be a standard phrase (if you Google for it). So I tried two Google searches to try to find out how he (Stephen Levine) uses the phrase (I haven't read his book):

• flow "Stephen Levine"
• flow "A Gradual Awakening"

Two of the quotes or paraphrases I found by doing this are:

• http://lifeparalyzed.blogspot.fr/2011/05/gradual-awakening.html

  He says everyone must start by focusing on the mind, as an observer, to watch thoughts, as they pass through the mind, and to begin to recognize the constant change, and flow, that is present, from moment, to moment. He warns, not to let one's self get pulled in, or get attached to any one thought, but to detach and let each moment unfold.

• http://www.spiritsite.com/writing/stelev/part6.shtml

  When we attend to the ongoing mind we see that even "the watcher" becomes part of the flow. The who that's asking "Who's watching?" is another thought-flash we see go by; there's "no one" watching, there's just awareness. When the "I" becomes just something else observed in the flow we see we're not different from anything else in the universe.

These seem to be using 'flow' to refer to a 'flow of thoughts', a sequence of thought, a progression or an ebb and flow of mental process ... watching flow is the same as watching thoughts.

This ("flow of mental observations") may or may not be exactly the same as "flow of arising and passing away of all conditioned things" ... instead maybe it's "flow of arising and passing away of mental awareness of all conditioned things". On the other hand I don't know how much emphasis you want to put on the difference between "the observed" (e.g. "all conditioned things") versus "the observation" (e.g. the mental awareness). I think investigating the difference or relationship between observed and observation, between objective and subjective, has been a big theme of western philosophy ... it may or may not be important to understanding Buddhism.

There's also this quote from http://www.personaltransformation.com/stephen_levine.html

When it's my cancer, I'm alone with my cancer. I have nobody, just me and my cancer, and it looks like there is no way out. When I realize it isn't my cancer, but the cancer, there is space to work on it. My depression, my cancer, crams me in, like being in a phone booth full of my life. You open the phone booth and see that everybody is standing outside of their phone booth. It's isn't my depression, it's the depression. When it's the cancer, I am in this flow of human-kind, with all the energy of four or five million other people going through the same thing at this same moment. You connect to something universal, which brings peace.

Here he may be using the word 'flow' to refer to "conditioned things" (i.e. human kind), or he might still be using it to refer to 'mental process' (i.e. saying "I am in the flow of mental process that's common to human kind").

When you quoted, "what separation from the flow feels like", that's not clear or is a bit ambiguous. I think that phrase implies that "flow" refers to observation rather than observed (maybe we don't separate from a flow of things, separate from human kind, when we meditate, but might separate somehow from flow of observations). Assuming that flow is referring to the flow of mental observations (and assuming it's even meaningful to distinguish that from the flow of observable/conditioned things), I think that "separation" might mean either suspension of observation (e.g. entering a jhana state), or a disassociation or dis-identification (i.e. some kind of awareness of anatta).

What is the meaning of 'awareness of the flow'?

When I read your question I actually think you gave a perfect answer, i.e. "...the continuous flow of arising and passing away of all conditioned things...".

I'm not too familiar with Stephen Levine or his book but it sounds like he is teaching about exactly this quality of conditioned phenomena. What is this quality?

Conditioned phenomena is also called compounded phenomena, meaning that they consists of other phenomena that again consists of other phenomena. In other words, we are here dealing with phenomena based on causality.

In Buddhism we have a Dhamma called the Three Characteristics of Existence, which are impermanence, unsatisfactoriness and uncontrollability. These characterize conditioned phenomena. In regard to the question, especially impermanence and uncontrollability is important here.

Impermanence shows that phenomena arise and cease. They come and go according to their respective causes and conditions. Uncontrollability shows that there is no stability or control to be found anywhere. One cannot exercise control over this flow. Mahasi Sayadaw calls it therefore oppressive and terrible. Oppressive is the incessant arising and ceasing of conditioned phenomena.

It sounds very much as what Stephen Levine is teaching about and what you yourself are describing. Now, the Buddha once said that its okay to use conventional language but that one should not be fooled thereby. In this regard, it means that all these different words (concepts) really just mean the same thing. Its just different ways of teaching it.

If we really want to understand what flow is then the practice of insight meditation should be undertaken. Intellectual knowledge only goes so far. With wisdom gained from insight meditation one will be able to see conditioned reality with ones own eyes.

In the Sabbasava Sutta (MN 2) the Buddha taught about 7 taints that should be overcome and with what method they should be overcome. The first taint should be overcome by seeing, i.e. The Four Noble Truths should be seen with ones own eyes. The truth about Samsara should be seen with ones own eyes, in here lies the incessant arising and ceasing of phenomena.

By gently letting go of everything—not through force, not by slaying it, but simply seeing all the content as passing show, as process and flow—we become the whole of our experience and open to our natural understanding.

It might mean that when staying in the present moment and not letting the mind straying into past or future even for one moment, Wisdom (natural understanding) will arise.

We can observe [with our practice] what anger feels like, what joy feels like, what separation from the flow feels like, what fear or worry feels like.

Separation from the flow, meaning that when the mind has wandered off into past or future one disconnects from ultimate reality and instead ventures into conceptual reality.

What joy, fear or anger feels like, means to know the quality of that object when it arises, as it exists and when it disintegrates. To thoroughly contemplate the objects qualities and distinctive marks.

[Hindrances] distract us from an even-minded awareness of the flow.

When hindrances are present one cannot clearly see reality as it has been plastered over with many different colors of dye (example given by Ven. Bhikkhu Bodhi).