Samsung Nexus S flickering problem

[secluded4me]

Hello,i have this flickering problem for a good while now...my phone just turns the screen on and off (not shuting down) just this turning on and off maybe at an interval of 10 seconds for a few seconds..it is just stressful at night seeing light on the ceilling,plus that i dont want it to affect my phone,maybe it's an application i forgot to close?.Thank You.
this is a direct link to what's happening to my phone.

http://www.youtube.com/watch?v=kx2QpLMGzNo