Normal or Faulty ?

[Musaali22]

I Bought an S5 , the octa core variant , whenever i open the video player and play a video , after that my phone slows down and whenever i drag an icon , it behaves abnormally , it keeps floating as i drag it . some times the phone becomes unresponsive and it stops working . PLEASE HELP ME , HAS ANYBODY EXPERIENCED THIS PROBLEM ? IT HAPPENS WHEN I PLAY A VIDEO AND CHANGE THE VOLUME BY SWIPING UP AND DOWN THE RIGHT SIDE OF THE SCREEN WHILE PLAYING A VIDEO OR sometime after LONG time of USAGE :'''( THE DAMN ICON KEEPS FLOATING AS I DRAG IT !!!