A state is a combination of an internal representation and the internal kinaesthetic feeling that goes with it. We describe a state with a label such as alert, sleepy, sad, cheerful, depressed, or happy.
A state is the result of both your internal representation and your physiology working together. The state you are in directly affects your physiology and therefore your behaviour.
Your internal representation creates the state you are in, and the state leads to the behaviour or physiology. Importantly, this relationship works in both directions — changing your physiology will also result in a change of state. This is why standing tall, breathing deeply, or smiling can shift how you feel even when the external situation has not changed.
Being in control of your state means you are in control of your body and mind — and therefore your results.
See also: What is Personal Power? | What is NLP?