What causes episodes of bradycardia in a person with anxiety?

Question: Hi I had all cardiac tests done and everything came back structurally normal. I passed my stress test achieving 90 percent of maximum heart rate. My Holter showed some pacs. Approximately 400 over 48 hours and 15 pvcs. What is concerning me is the fact that I have episodes of bradycardia where my heart rate will be around 55bpm. My cardiologist insists that my heart is very healthy. I suffer from anxiety especially since I've had palpitations. Also I get episodes where my heart starts racing around 170bpm especially after doing minimal exertion. For example climbing the stairs. This worries me the most.

Today I did a lot of walking to get some physical activity and I felt great. However, after I went in my car and drove to my parents house I started getting fast heart rate when I got out of the car and started walking again. Could it be anxiety causing these palpitations. I've had so many tests done on my heart and everything seems to be normal. I don't understand why I would get palpitations after exercising and resting

Doctor thank you for getting back to me so quickly. These symptoms are driving me crazy sometimes. Today was my daughter's birthday so I took your advice and did lots of physical activity and took her to play all day and then to the shopping mall and we walked for a while. I felt good. Then after resting and getting up again, tachycardia started up again I could feel palpitations just from walking from my car to my mother's front door. Is this normal?
Also can anxiety be a cause of bradycardia? I heard that bradycardia can be one symptom of prolonged anxiety?

Hi doctor I have one more question. Is there a reason why sometimes I will have more bradycardia than others. For example on some days I will feel a slow pulse even when standing and on others it is more pronounced. On days when I feel it slow it also feels weaker.