What causes a slow heart rate during menstruation?

Patient's question:

Detailed medical condition and consultation purpose:
Dear experts and teachers,
I have experienced multiple episodes of bradycardia over the past year, with a heart rate of approximately 54 beats per minute (accompanied by stomach discomfort). This usually occurs on the first day of my menstrual cycle, and my heart rate returns to around 64 beats per minute by the second day. I often suffer from iron deficiency anemia and don’t exercise much. Is this bradycardia a condition? (Is it related to my mood? I’ve been quite depressed over the past year.)
I look forward to your reply. Thank you!!
First follow-up question: Thank you for your reply! Regarding the abnormal sensation

Doctor's answer:

Iron deficiency anemia is recommended to take oral iron supplements: common medications include ferrous sulfate, ferrous succinate, ferrous fumarate (ferric acid), etc. Yangxue Yin is made from multiple traditional formulas, which has no stimulating effect on the gastrointestinal tract and is recommended for use. When taking medication, avoid tea to prevent iron from being precipitated by tannic acid and not being absorbed.
Supportive treatment: Enhance nutrition and increase intake of iron-rich foods. Anemic individuals should pay attention to eating more high-protein, vitamin B, and vitamin C-rich foods, as well as iron-rich diets in their daily diet. Beneficial fruits include apples, jujubes, lychees, bananas, etc. Additionally, consume more foods such as black fungus, shiitake mushrooms, black beans, sesame seeds, etc., which are beneficial for blood nourishment.
If oral iron supplements cannot be tolerated or if changes in the normal anatomical sites of the gastrointestinal tract affect iron absorption, iron injections can be used. Iron dextran is the most commonly used injectable iron. The first dose must be 0.5ml as a test dose. If there is no allergic reaction after 1 hour, the full therapeutic dose can be administered. On the first day, give 50mg, and then 100mg daily or every other day until the total required amount is met.