Anxiety can be best described as an adrenalin / fearful thinking loop. So, both thinking and the physical symptoms of a heightened release of adrenalin are present. Anxiety is a normal reaction when a person is under threat. The physical symptoms are normal as is the need to take flight. It is nature's way of keeping us safe.
The term “suffering from anxiety” means that a person creates an anxiety response that is out of proportion to what the threat is or creates it when seemingly there is no threat that is rationally obvious.
Anxiety can be stated as “over-protection” by the mind. It is a learned response from one's experiences. You don't have a “mental illness”, you are not “going crazy” or “losing your mind”. It is simply a subconscious learning and what you learn can be unlearned and replaced with a learning that serves you better. The ideal learning would be how the average person would feel and behave in a particular situation who didn't have an anxiety problem.
Fear is the perception that there is some immediate danger, the mind gets us ready to fight or flight. Human beings are not the only species to experience fear, we are the only species where our imagination can play havoc with this primitive response and cause us to experience fear when it is not necessary or create an exaggerated fear that is totally inappropriate in the situation.
Worry is the fear of something that may happen in the future. Worry is the cornerstone of anxiety for many people.
The presence of a heightened release of adrenalin is central to anxiety. We have two adrenalin glands, one sits at the top of each kidney. This is why the first sign of an adrenalin rush for many people is the uncomfortable feeling that starts in the stomach. The feeling expands and you heartbeat gets faster, your breathing speeds up, you start to sweat, etc. You are being primed with the energy to fight or flight.
While many people believe that anxiety is always triggered by the mind, physiological factors can also trigger anxiety and panic attacks. See the posts where l explain how physiological factors can affect anxiety and then comment on cognitive factors.