Stuck

So today, I tried writing my UC Prompt 1 essay. I wrote about 1 1/2 paragraphs and then... BAM. I suddenly did not know what to write. I sat at my computer for around 30 minutes, gave up, watched t.v. to try to arouse some inspiration, came back to my computer, and continued this cycle for about 4 hours. I have not written a single sentence since. I honestly don't know what is wrong with me. It's driving me crazy. I know what my theme is, but I just can't think of the right words to type. I'm so worried now. If I continue this cycle, I'm not sure if I'm going to finish my essays in time. I feel like my brain is fried. Maybe I just need some sleep. By tomorrow, maybe I'll be able to think of something to write.