One cause of sleep disturbance not mentioned here is adrenal fatigue (hypoadrenia), a frequently overlooked or misdiagnosed condition. Most doctors, if they look for adrenal malfunction at all, are testing for Cushing's Disease (hyperadrenia) or Addison's disease (extreme hypoadrenia). But adrenal fatigue, falling somewhere in the middle of the 7 stages, can have life-changing effects. It did for me, until I read an article that enabled me to self-diagnose and seek treatment. Key symptoms for me were morning fatigue, nighttime sleeplessness (sometimes until 3-4 a.m.) and odd energy fluctuations. Due to cortisol disruptions, I couldn't get out of my own way until about 5 p.m. - the close of business! I went through 28 months of unproductiveness, exhaustion and frustration. Look here for more information:

http://tinyurl.com/6wu3w9

I had a problem falling asleep from the time I was going through puberty until post college.  When I started working after college I had a really hard time with a full day schedule since I only slept two or three hours at night.  That's when I started self hypnosis.  I learned how to fully relax my mind\body, breathe deeply, visualize a peaceful environment, and  focus on the calm, instrumental music on my cd player.  At first it took me about an hour or so to go to sleep like this but eventually I could sleep in 3 minutes or less.  I no longer need the music as I can put my mind and body in that state almost instantly.  

University of Texas recently confirmed what I learned long ago from my herbalist grandma (I'm 72).  Sour cheery juice contains large amounts of melatonin and many other beneficial phytogens.  I'ved used it for years with vitamin C to reduce muscle fatigue after hard physical labor and to assure a good restful sleep.  My guess is would be hard to overdose on melatonin in cherry juice.

Just a slight warning about hops--it is a sedative but can cause depression in some people when used over a long period of time.  Valerian has worked well for me with no hangover effect.  Passionflower is also a good herb for insomnia.  Lemon balm and scullcap are also very relaxing.  

I suffered from insomnia for many years, mostly from living in thin-walled apartments where neighbors would blast their T.V.s or stereos all night and garbage trucks would tromp through the neighborhood at 4 a.m. waking up my kids and every baby in the area.  (In my crowded neighborhood I could hear them all crying through the opened summer windows right after the crash, smash, beep-beep-beep truck noises).  Sometimes the anger at having to deal with the artificial night-noise would keep me up for the rest of the night.

If insomnia is caused by your restless mind, try herbs or other alternatives, but if it comes from the outside world, all you can do is try to move to a quieter location.  I think a lot of insomnia is caused by people living in overcrowded, over-noisy, over-lit situations that are completely unnatural to getting a natural night's sleep.

In the list of underlying causes of sleep disorders, let's not forget that for many men of middle-age and above, prostate problems can cause constant sleep disruption.