Talk to General Physician on Heartbeat Increases

my sister is facing a problem from a month...It got worse yesterday....her heart beat increases suddenly, breatg gets shorten and then she fells down...her body gets paralyzed for some minutes...she feels anxiety and depression when this condition attacks.... we had her echo and ECG test yesterday... everything is normal according to doctor....she is using andreal medicine for hearbeat and a muscle relaxer...but she had this attack this morning again. we are unable to figure out the reason... please if anyone can help.let me know