I always found the flow and berserk state fascinating and extremely interconnected. I don't know if you ever experienced a flow state, but let me describe it to you.
In a flow state, your subconscious and conscious merge into one. No more self-talk nor subconscious feelings. The normal way you brain work stops. There is no other thing that a very deep focus and awareness, there's no thought that can escape your control. In a flow state, you are in control -no, you are the control -.
In a flow state, you don't fear - you act -. Your field of vision increases, colors are more vivid, sounds are clearer, everything becomes more objective and easier to perceive. Reality becomes slower than you.
How many times did I experience that? Well, like 3 times in my whole life. I don't even know if that is what people really mean by "flow". But you find yourself being very smart. The problem is that I couldn't maintain that state, as soon as I became aware of that, my background subconscious noise started to gain territory in my mind.
Let's be clear here, I can think without representing thought as sound/voice inside me, therefore I'm somewhat aware of what my lower level not talking self is doing. I believe that part of the human physique is what regulates/restricts our behavior and capabilities.
If you start thinking something, you know what you are going to say before thinking it in sounds or images. If you just observe those mental processes without converting them to sounds/words you can start being aware of a deeper self you have.
We all have low level inner conflicts, fears, insecurities and desires. It's what makes us animals that can transfer survival knowledge through our DNA.
We are stupid monkeys, we act based on emotions. You will later justify your actions using your critical thinking, but that's just a proof you are a low class monkey.
Your mind tries to give you an identity, and a set of behaviors that you blindly accept and follow. We can't resist that for the most part. And your power of will just becomes another illusion, and your identity just a jail you feel proud of being inside.
If you are aware of it, you can influence it:
Change the rules on what controls you and you will change the rules on what you can control.
Revolver (British-French crime thriller film)
Your subconscious is pretty dumb. Really dumb. Is programmable and highly impressionable by emotion. If you are not careful you can fall in a lot of mental traps and loose your fragile true identity trying to differentiate what comes from you and what comes from this inner evolutionary machinery.
Your subconscious never stops, it's always there consuming resources, in the same way that those useless windows updates run in the background slowing down your computer.
People talk about emotion or the hearth. Those emotions you feel are the chemical representation of your subconscious. If you ever had an intention of suppressing your emotions you know that doesn't work. If you ever wanted to feel something you know that does work.
What I'm trying to say is that by focusing in what you want to feel you can start feeling it. By feeling something, you change your inner chemistry. In that new state, in theory, we are in a position to modify or use the subconscious.
If you can focus with your feelings and the normal thought you are used to think with. You can increase you cognitive abilities. This means, that you are not in a conflicting state of being.
I love the concept of someone going Berserk. There is something captivating in the possibility of being posses by an one-dimensional flow of action. But operating only in one layer of thinking/action will destroy the carrier. We are the carriers of different ideas, and that variety is what keep us alive. But a Berserk is an defective carrier of just one objective.
His (Odin's) men rushed forwards without Armour, were as mad as dogs or wolves, bit their shields, and were strong as bears or wild oxen, and killed people at a blow, but neither fire nor iron told upon them. This was called Berserkergang.
Laing, Samuerl (1889)
As you may appreciate, the Berserk term refers to a very formidable warrior who doesn't care about anything else but to kill, not even his own life or integrity. And from that lack of care they derive all his inhuman strength.
I bring this extreme and unhealthy example of one-dimensional behavioral flow, because I think those warrior were able to silence all superficial and inner thought. Even if that was induced by substances, it shows that is possible for a human to do. Also it may explain why I was able to have at least for a while such mental power and clarity.
I think we all must care about the sustainability of our behaviors. How sustainable an habit or way existing is in the long term.
For me the only real way of having a sustainable good performance, is to increase our focus and emotional regulation. And treating those two factors as one, in the same way that when we workout we exercise and take care of our diet.
Practice concentration and emotional control.