Sleep disorders consist of:

1. Insomnia.

This malady often affects almost people of all ages.  Regardless of whether it is acute or chronic insomnia, the cause can be the following:

• 1.1 Psychophysiologic Insomnia.  Patients in this category usually suffer from racing thoughts before bedtime, as they tend to believe that they have difficulty sleeping.  This actually makes it even harder for them to fall asleep.  Some of these patients are treated through Cognitive Behavioral Therapy for Insomnia.
• 1.2 Paradoxical Insomnia.  Patients in this group misunderstands and worry that, because of their insomnia, the condition will affect their health.  Some of them needs sleeping aids – especially medicines in the benzodiazepine class – every night and become dependent on the drugs.  Worse, they sometimes require higher dosages for the same effectiveness, as they are now more tolerant to the medicines.
• However, patients suffering from paradoxical insomnia, after they have been further diagnosed through polysomnography, may discover that they can actually fall asleep at the normal sleep onset.  But, rather, they may have been affected by Sleep Microstructure that detrimentally impacts their quality of sleep.  So, the length of their sleep can appear to be sufficient but the patients still feel sleep-deprived, leading them to believe that they have insomnia.
• 1.3 Insufficient Sleep Syndrome. This condition is often found among the youths, especially now that the Internet or smart phones are widely popular.  Patients in this group tend to stay up rather too late.  Though they do not have any problem with sleeplessness, what follows is that the patients get up late and are affected by Non-Restorative Sleep; which can impact their studies.
• 1.4 Insomnia Secondary to Medical Problems.  As the name suggests, patients in this category cannot sleep because of some other medical issues.
• 1.5 Insomnia Secondary to Medication. Similarly, some medicines can be central nervous system stimulants which cause sleeplessness.
• 1.6 Idiopathic Insomnia. This is sleep disorder due to indeterminate cause. 
• 1.7 Others.

2. Central Origin of Hypersomnolence

Patients in this group sleep too much due to some disorder in their nervous system.  So, the condition should be further investigated.  However, before classifying a patient into this group, it is proper to ensure that the patient has actually had sufficient sleep and is not actually affected by insufficient sleep syndrome.

Most central origin of hypersomnolence patients exhibit excessive daytime sleepiness, which can be a result of something like Narcolepsy.

Narcolepsy patients, apart from excessive daytime sleepiness, some of them may suffer from head nodding syndrome, knee buckling, or cataplexy.  All of these conditions are brought on by various stimulants – such as humor – and can cause acute loss of muscle tone.

Other symptoms found in narcolepsy patients include sleep paralysis – a condition known as preserved consciousness which makes it impossible for the patient to move and often occurs when the patient wakes up while still feeling drowsy.  Some may call this “being possessed.”

As for hypnagogic hallucination, it is found among narcolepsy patients as they hallucinate while still being half asleep.

3. Circadian Rhythm Disorder.

• 3.1 Advanced Phase Sleep Disorder.  This is found among some of the elderly, as they tend to fall asleep early in the day but also wake up very early; while some others may experience waking up in the middle of the night as well.
• 3.2 Delayed Phase Sleep Disorder. This is often found among the youths, as they sleep and wake up late.  When they have to get up early, they may feel sleepy at school or at work during the daytime.
• 3.3 Irregular Sleep – Wake Rhythm. This is sometimes found in patients with neurodegenerative disorders – such as dementia.
• 3.4 Non 24-Hour Sleep – Wake Disorder (Free Running).  This is often found among patients who are also blind, especially those with total blindness.
• 3.5 Jet Lag Disorder.

4. Parasomnia.

• 4.1 Non – Rapid Eye Movement Parasomnia for example, night terror, sleep walking, sleep talking, sleep drinking.
• 4.2 Rapid Eye Movement Parasomnia such as REM Behavior Disorder which is often found among patients with synucleinopathic disorder – for example, multiple system atrophy, dementia with lewy bodies, and idiopathic Parkinson disease.

Other disorders such as

5. Sleep Related Breathing Disorder when breathing ceases during sleep – for example, obstructive sleep apnea, obesity hypoventilation syndrome.

6. Sleep Related Movement Disorder such as bruxism (teeth grinding during sleep), periodic limb movement disorder.