A 25-year-old woman presents with complaints of palpitations, exercise intolerance, fatigue, near syncope, and syncope. She was completely well until 6 months ago, when she contracted a severe flu-like illness, after which her symptoms began and have continued since.

Her 12-lead electrocardiogram and echocardiogram are normal, as are her thyroid profile and complete blood count. Findings from her physical examination are normal, except that when going from sitting to standing her blood pressure decreases from 110/70 mmHg to 100/60 mmHg and her pulse goes from 80 bpm while sitting to 120 bpm while standing.

Which of the following is the most appropriate treatment strategy?

1. Cardiac rehabilitation.
2. Instruct to the patient to consume 3L of water/day.
3. Ivabradine 5 mg OD.
4. Propranolol 10 mg tid.
5. Pyridostigmine 30 mg tid.