What Causes Pain In Head That Goes Down To The Eye?

i have a sharp on and off pain in the right side of my head, feels like it is inside my brain. the pain goes down to my right eye then goes away and comes back in a minute or so. it just started last night (april 19, 2011) when i close my eyes the pain goes away slightly, but the pain has been more constant in the recent hours. what do you think it is? and what should i do? also is it a very serious problem?