A Proplem with my screen!

Hi, I have this problem since a month:

Suddenly, the display's light becomes flashing on the right and left sides, and after a while, the whole display dims gradually and doesn't respond to touches.

When that happens. I have to press the lock key in the back twice to take me to the lock screen where I have to enter the pattern again.

'''NO SPECIFIC TIME FOR THIS PROBLEM TO OCCUR

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and some times it takes two days to see this problem again.

But sometimes it become so annoying and happened rapidly so I can't do any thing with my phone.

Please help me, is it a screen problem ???