4am and I'm Distracted

OK I am officially a writer.
I am supposed to be studying for a big exam that I have on Monday. My Professor would be so proud of me. I was on track working on the third case study; when all of the sudden...
An idea of a book has popped into my head. Its a simple one and would support my work with battlefield vets. But Really!  I don't need this right now. I have a quiet house and the isolation that I need. I'm supposed to be absorbing information but I'm as empty as the dry sponge on my kitchen sink. 
Why do these fantastic ideas arrive at the times when we are busy?
One of my author friends posted a funny the other day:
I'm an excellent plotter in the shower.
I'm an excellent character developer in the car.
But put me in front of the computer with nothing to do and nothing.

So I have filed my idea away, hoping the inspiration will stay fresh where it's stored.

Back to my studies...