Why does anxiety occur?

It is normal human emotion and affects animals as well. Visit this site for more information, though it may not provide a satisfactory answer, as there may not be one. https://medlineplus.gov/anxiety.html#:~:text=Anxiety%20is%20a%20feeling%20of,before%20making%20an%20important%20decision.

Anxiety is caused by fear & worry. This is what goes on in the brain. These are the emotions involved. The physical symptoms associated with anxiety are due to release of the stress hormones, adrenaline & cortisol. Stress management coaching / therapy can be very helpful in dealing with frequent anxiety.