I sometimes notice fluttering like something happens for seconds in middle part of chest just below where food pipe ends at random point of time in whole day, should i be concerned about it? i am non-smoker, non drinker but have sedantary lifestyle?

It is probably palpitation with ectopic heart beats, sometimes triggered by caffeine. That symptom is not consistently with GERD (reflux). If it happens almost daily with high frequency you need to see a doctor. If it happens just once in a while, you have nothing to worry.

Yours is a good question, and you instinctively know that you should investigate this change to the way your body is behaving. You make also have put your finger on a clue to the diagnosis in that you are not exercising as much as you know you should to stay healthy. Why not go and have a physical check up an follow the doctors recommendations.