Hi,
heart rate variability in a day is common-so don't worry about fluctuations in heart rate.Also don't be tensed.You should worry if you having symptoms like
chest pain,breathlessness,giddiness etc.Just follow advise of your Cardiologist doctor and be on regular follow-up with him.Try to relax by doing
meditation,listening to soothing music.Hope this information is useful to you.Take care and I wish you good health.
Dr.Prashanth