Pain on his upper stomach area can be caused by various reasons, including minor problem such as indigestion
or stress, to peptic ulcer disease
& serious medical emergencies such as a heart attack
The symptoms as mentioned in your post suggest that it might be due to angina.
Pain in upper part of stomach can be attributed to radiation of chest pain.
Presence of pallor, cold sweats & sleeplessness
may also indicate a cardiac cause.
Investigations like an Electrocardiogram or Stress Echocardiography
can clinch the diagnosis.
So, it will be better to consult a Doctor & get a physical examination done to find out the exact cause. So that proper management steps could be taken.
Wishing your Dad a Good Health. Let me know if I need to clarify further.
Thanks & take care.