Frustrated (metaphorical) orgasm

I feel like I'm on the edge of writing a really good first draft of a really good statement of purpose for grad school apps, and two things keep happening: either I get tripped up on the ideas in my head and can't quite get them on paper coherently, or I run out of time to devote to the process once I'm on a roll. It's like it's almost there, almost, aaaalllmmooossstt... and it's gone. I'm actually excited in writing this draft, and that alone is a good thing. I'm not hating every second of it nor am I dreading letting someone else read it. If only I had more time on my lunch break...