The fact that 24 hour Holter monitoring & ECG has not shown anything rules out the any Cardiovascular causes for the symptoms.
The symptoms in your friend can be due to:
1. Anemia- either due to decreased Hemoglobin
production or deficiency of certain nutrients like Iron, Vitamin B 12, Folic acid
, etc. which helps in blood formation.
2. Inadequate hydration status & electrolyte balance of the body.
3. Any fluctuation in the blood sugar levels.
& metabolic causes.
5. Stress, inadequate sleep, etc.
Investigations like complete blood count
, estimation of blood sugar levels will be helpful to rule out any pathological cause for the symptoms.
And it is also needed that your friend take certain precautions regarding diet & lifestyle, such as:
1. Take soft, plain, non-spicy foods
2. Drink lots of water to maintain adequate hydration
3. Avoid fast food.
4. Avoid smoking & alcohol.
5. Keep away stress..think positive.
6. Exercise regularly & practice meditation
Wishing a Good Health.
Thanks & take care.