People have a fear of doctors for a variety of reasons. You may fear hearing "bad news" from the doctor. You may regularly experience a rise in blood pressure on visiting the doctor, and fear the doctor will exaggerate its importance. You may be afraid of needles and the sight of blood.
If you are claustrophobic, you may fear waiting in a small examination room. If you experience panic attacks, you may fear any situation from which it is inconvenient or difficult to leave quickly, be it a haircut, a shower at the health club, or a visit to the doctor.
My experience in helping people with a fear of doctors is that to try to hide these fears and "tough it out" almost always makes the anxiety worse. So I recommend that when you call for the appointment, you speak with whoever keeps the appointment schedule and tell that person, briefly, that you sometimes have difficulty with doctor visits because of anxiety or phobias; explain briefly what that fear is; and ask them to help make it easier for you.
If you just don't know how to explain your problem so others will understand, you can liken it to claustrophobia, a condition in which people become very frightened whenever they are in a closed, small place. Since most people seem to know what claustrophobia is, this comparison can make your explanation easier.
Some of the arrangements that my patients have made included: shorter times waiting in the examination room; taking several measures of blood pressure throughout the visit, knowing that it will likely go down as you get used to being there; having a glass of water available; having a staff member check on you while you wait for the doctor; or having a support person with you. I'm sure there are as many possible arrangements as there are worries. I once worked with a woman whose fear of the dentist centered on seeing his white coat, so we arranged for him to wear street clothes for her first visit.
Beyond the specifics of these arrangements, it can be very helpful to know that the doctor is aware of your anxiety, and that you can talk about it, rather than try to hide it and fight it. In my experience, the effort to hide and fight the anxiety is often the most significant obstacle to recovery. This is the basis of the Anxiety Trick.
People often worry that the doctor won't want to be bothered, or that the doctor's staff will find their concerns ridiculous.
My patients have generally found that, once they talk to their doctor about this, the doctor is usually more understanding than they expected.
But if your doctor really doesn't want to be bothered, find another doctor!