Understanding the physical aspects of anxiety is important, but the condition is also a psychological condition and understanding the condition from a psychological perspective is also important.
When adrenaline is released into our system and no threat is present, we will still react to the adrenaline. Anxiety is a psychological response to this heightened state of a threat when there is no threat. Despite the lack of an actual threat, the mind is forced to deal with the extra adrenaline and the emotions it triggers.