Sleep is an area of special interest for me because in my years as a Psychologist I have seen no single issue have a greater impact on my own personal contentment and the contentment of my clients than sleep. Recently I have been thinking more about nighttime wakefulness (i.e., waking in the middle of the night after sleeping a bit, and before the alarm goes off, and being unable to fall back to sleep) because it is something I have been experiencing more frequently. It's probably no surprise then that my browser curated this article for me:
Shuteye and sleep hygiene: the truth about why you keep waking up at 3am, by Elle Hunt (The Guardian)
The article is fairly dense, for such a piece, so notice that it lists three general categories of issues to consider when examining your sleep waking: diet, behavior, and cognitions (thoughts/mentality). There are, of course, other things to consider (e.g., stress contributes to sleep disturbance), but these are good places to start. I would make a list of possible causes and start to test the causes, starting with the most likely causes, or the simplest ones to test. I also highly recommend talking to your doctor or qualified mental health professional about sleep problems. The conclusion was practical, if not particularly comforting: normal people experience sleep issues during their lifetime. Acceptance of the normal rhythms of life (so long as they are determined to be normal, and not indicators of a larger issue) is one of the most effective way of dealing with them and thus promoting a sense of satisfaction and contentment.