Can't sleep - or you sleep, but awaken feeling like you did not sleep well?  Long ago(sorry I have not written about this earlier), a major sleep study was reported to have found that human REM sleep cycles are generally 45 minutes duration.  This is the time of your sleep in which you typically dream and experience the most restful portion of your sleep.   One should not wake when experiencing REM sleep.

     Humans have multiple REM cycles per sleep.  I found(yes, I experimented) that if I had seven hours of sleep, instead of six and 3/4, or seven and 1/2, I awoke feeling tired and restless.  When I adjusted my sleep times to reflect a multiple of 45 minutes, I awoke refreshed, even if I had less sleep time than usual.  Have you sometimes nodded off, or napped, to awaken feeling much better?  If you think about it, you may find the reason is a well-timed REM sleep cycle, and not Ambien or Rozerem.
     Not everyone will have the same REM time cycle, so experiment with times of approximately forty to fifty minutes, and adjust your total sleep times to a multiple that fits your body's requirements.  Sleep tight!