Sometimes our brains are not kind to us. Many people will lay awake through the night while their mind imagines all kinds of scenarios. Concerns about finances, work, school, health, or family matters can often causes insomnia, because the mind stays active and cannot switch into sleep-mode.
If you are under a lot of pressure at school or at work, going through a bad relationship or chaotic breakup, recently lost a loved one, or have faced some sort of trauma, it will take a long time for the cortisol and adrenaline to leave your body. Try doing relaxing exercises, like yoga and meditation, and treat yourself to a little kindness. Eventually, your sleep cycle will return to normal.