Hi. From your description your friend seems to have suffered from mild Covid. However post Covid or any viral illness deconditioning is common. There may be exaggerated increase in pulse rate with minimal physical activity. It slowly settles down after 6-8 weeks.
Next Steps
It is worth checking a few basic things which can give a clue to the cause of palpitations and chest pain like ECG and basic blood tests like hemoglobin,
thyroid profile and
vitamin DHealth Tips
Seek consultations with a doctor for detailed evaluation if symptoms are very disturbing