Palpitation even after ASD closure.

I had undergone surgical closure of ASDs in Oct 2016 at Asian Heart. Since then I'm always very concerned as my heart rate triggers immediately. It spiked after climbing even 2 floors. And since couple of days I'm having a dangerous feeling of heart beat skipping, earlier it was once in two days but now the frequency has increased. I prefer to do 2d echo every 6 months, i did it a month back and Dr says it's normal. Only observation was Grade 1 diastolic Dysfunction. I'm very worried about this skipping beat situation as whenever that happens i go into a fear mode for sometime. Need suggest if this is something to worry and need further investigation. It usually happens in evening only. I'm on seloken xl 50 1 at afternoon and Telmisartan 20mg 1 at night. I'm able to walk 4.5 KM in 50 mins without any issues. Did serum potassium, serum calsium and serum magnesium test. Potassium and Calcium cake normal and Magnesium High 5+ but dr says its incorrect.