Anxiety can be defined as the anticipation of a future threat. Fear is defined by a well defined threat.
Anxiety is can also be brought on by medical conditions so it would be a good idea to check into any of these.
Hyperventilate Vitamin or mineral deficiency like B12 /Vit D.
These are just a selection. I am only writing from experience and am not medically trained so you must take full responsibility for your own health.
We have all got the fight and flight response within us, in built for our safety. The good old Amygdala, the part of our brain so responsible for stress, tension, anxiety, fear and more, senses something wrong and goes into action to activate our body to be able to get to safety. As the Amygdala is so helpful he retains the memory of this perceived threat, all be it little or large and re enacts the situation if ever something similar happens in the future. So for example, you fell off a swing when you were young, the amygdala remembers the incident and this will explain why you feel anxious or stressed about getting on a swing in the future.
Unfortunately, in this day and age, the most common threat is a PSYCHOLOGICAL THREAT.
Going on from this our anxiety/stress can also be caused by personality traits.
Being a Highly Sensitive person ( more on this topic later on) almost always goes hand hand in hand with anxious feelings.
Some people put a lot of pressure on themselves because of their need for approval or perfectionism.
Again some people like to be in control so put pressure on themselves to get everything done themselves without help.
I am afraid I am going to say it the our anxiety of today could be because of experiences of our childhood whether they are happy or sad.
Anxiety and stress can do damage to our minds, body and health so we all need that toolbox to help us enjoy our lives instead of fighting everyday.