You may ask yourself "why do I fall asleep?" and "why do I wake again?" Sleeping and waking happen in a dynamic balance of two sleep mechanisms, the homeostatic process and arousal threshold and two wake mechanisms, circadian rhythm and autonomic nervous system activation.
In order for you to get a good night's sleep these mechanisms must be in balance with each other.
Now normally when these cycles get out of whack the body kicks in to survival mode and tries to right itself.
If one of these sleep or wake mechanisms gets defective or irregular, then sleep will become unstable and out of rhythm.
Homeostatic sleep process What this means is the longer you stay awake, the sleepier you get.
If you stay up for long periods and continue to stay awake, the body will eventually force sleep upon you.
This could be dangerous if say you are driving or operating heavy equipment.
Arousal threshold After you fall asleep, the arousal threshold kicks in.
It is an internal biological mechanism that helps to preserve sleep.
Located about midbrain in the thalamus, it filters out stimuli such as noise to shield the brain so you can continue sleep.
If an external noise or an internal stimulus, like pain, manages to break through the filter you will wake up.
Ciradian rhythm This is an internal alarm clock that everyone has.
Your body is set to a 24 hour clock that goes to your routine.
So if you get up at say 8 AM every day for work, your body learns that and will get you up about that time every day no matter how long you slept.
This is why if you have ever stayed up really late and finally could fight sleep no more, you get up automatically at your set time.
That's the automatic alarm clock your body sets.
Autonomic nervous system activation This part of your nervous system is what keeps you awake when you finally do get up.
This is part of your sympathetic nervous system which can hinder sleep, get you riled up and angry or create a conditioned response.
A lot of sleep problems are a result of autonomic nervous system over-activation.
Stimulus can be external such as caffeine, stimulants, heat or noise.
Internal stimulus would be things like fear, worry, anxiety, pain, and anger.
It can get to the point that the bed causes a conditioned response like if every time you go to bed you start worrying about something, the bed could trigger this response every night.
Understanding the different mechanisms the body has for the sleep and wake cycle can help treat the specific problem and get your body back in the right rhythm to get a good night's sleep.