I would like to share how I personally managed to stop my brain from racing, and to become physically and mentally relaxed.
You can manage this by holding your breath, and observing when your CO2 levels in your blood becomes unbearable (the feeling of choking). At that point, exhale slowly, and take a minimal amount of oxygen in. If your body panics, take more oxygen in. The goal is not to feel suffocating, but to hover just above that point in a relaxed way.
You will notice your body does not need much oxygen if you don't move. And by having little oxygen, you 'tell' your body to relax even more. Soon, you will notice that the biggest user of the oxygen is your brain. With a little practice, you can disconnect most if not all thought patterns. Slow down your thinking. Slow down your feelings. Just observe.
Soon you will have minimal flow (dualism) in your body, your thoughts, and your feelings. All that will remain is consciousness. When you totally 'see', deeply understand, that 'you' ARE that consciousness, you can start using your body, thoughts, feelings again. But now from a perspective that those things (body, thoughts & feelings) are not you: but are observed by consciousness. Not 'your' consciousness. Ego does not exist, but in your brain, as a construct.
It is my personal experience that that consciousness is 'in the background': everywhere. Our bodies/thoughts/feelings are just point of views: for the One Consciousness that permeates through all things: humans, animals, plants, rocks, the sun. Perhaps I can make an analogy with paper (consciousness), and the molecules, the body/feelings/thoughts that 'write' on this paper: manifesting themselves on this paper, in this universe. Our ego thinks that we are the drawing. But we are the paper. And there is no 'we'. There is only paper. And things manifesting on that paper. Which we then call 'me'. But in the core: its only paper: the cosmic background consciousness.
Its hard to talk about the experience in words. I hope this makes any sense to anybody.