Insomnia is really one of the easiest conditions to cure with meditation; the cure is to forget the nonsense that says you must fall asleep. From a meditative point of view, it would be great if you could stay awake all the time in order to meditate. It is actually quite refreshing to meditate all night; I have done so on several occasions and have felt no negative impact at all. The problem is we are usually anxious about falling asleep, watching the clock and worrying about getting the right amount of "quality" sleep. In truth, the waking state has much more quality to it than sleep, provided one's mind is clear and free from defilement.
The best way I know to overcome insomnia is to train yourself in lying meditation. Just lie on your back or side and watch the stomach rising and falling. As it rises, say in your mind "rising"; as it falls, say "falling". If you feel worried or anxious, just say in your mind "anxious, anxious" or "worried, worried" until it goes away, returning to the rising and falling of the stomach when it does. If you practice this regularly with an attitude of acceptance towards staying awake even far into the night, you should find your sleeping pattern returning to normal. Of course, this assumes you are not taking drugs like caffeine (coffee) or anti-depressants; otherwise, insomnia is a problem we should not have to suffer from at all.