[Vemnagelignc]

Occasionally have the same problem although I'm usually out within seconds.
About the only thing to do, I found, was to make sure I was really comfortable and to not worry about getting to sleep - more you dwell on it, the more it'll keep you awake.
Sometimes it helps to visualize a blacknes/blankness in front of your eyes as often insomnia is due to different things churning over in your mind.