I always figured it was a mix of sleep debt and exhaustion.

Turn that around though and ask what are non-military people doing to make going to sleep more difficult and it seems straightforward. Sitting all day, not getting enough exercise, alcohol (not saying the military doesn't drink - been to some fairly wild parties on base housing, but 'on duty' I don't think they do), don't keep to a regular sleep schedule - and our diet's pretty bad.

But who's going to write an article about how not to go to sleep?