Sudden Panic Attack. Please guide me.

From the last 3 days, i am having heaviness in lower abdomen either in left side or either in right side. But most of the time i felt right sided heaviness in lower abdomen. Today i felt firstly on left sided, then after having lunch slowly it had turned to right sided lower abdomen, i felt heaviness in right lower abdomen, heaviness in right side throat, burping increased, which gave me some relaxation. All was fine till 1 hour before, suddenly i had to go downstairs from my 2nd floor office, so got my work done at the ground floor, and returned to my office after climbing the stairs. Within a few minutes i felt some uneasiness, nervous and i felt very discomfortness all over the body, i felt i am out of control, getting alots of burping and uncontrollable tensions. Now i am feeling light normal, but facing only heaviness in right lower abdomen. Panic attack is now normal. But i do not know why it happened suddenly, i am not in depression or anxious.Please guide me.