Screen flashing in email apps

Hello,
Can anyone help me please, I have a Samsung Tab 3 10.1 screen and it is 1 year old. Recently I have noticed that when I am doing emails using either of the apps that come with the tablet, after a little while the screen flashes black then back on. I don't lose any of the work I have done and I haven't noticed the screen flash when on the internet, only in email. Saying that, I got to end of this message and the screen flashed before I submitted it so maybe it is a general fault with the screen light? Does anyone know what can be the problem here please? I am wondering whether I should exchange the tablet whilst it is still in guarantee but obviously I don't really want to do this as it involves so much work saving things, apps etc. I have run an anti virus check but that hasn't come up with anything and the screen still flashes. Any help here would be gratefully received. Many thanks in anticipation. Sandra