Through osmosis (water movement from a low solute concentration to an area of high solute concentration) water is reabsorbed back into the blood from nephron tubules in the kidney. This maintenance of water concentration in the blood is essential for maintaining blood pressure and is affected in nephritis. Diagnosis
The cardinal symptom in Epstein syndrome is thrombocytopaenia with giant platelets (macrothrombocytopenia). A peripheral blood smear is taken from the patient and a light microscope is used to these identify giant platelets. Leukocyte inclusions are also examined for, because approximately 41.1% of R207 mutations have leukocyte inclusions. These are often abnormal neutrophils with a small size of approximately less than 0.7 um and have an abnormallocation on the non-muscle myosin heavy chain IIA (NMMHC-II). These inclusion bodies have RNA and no DNA. RNA in these inclusion bodies can be located in immunofluorescence analysis with the anti nonmuscle heavy chain IIA antibody.Hematology analysers or a hemocytometer can be used to determine the amount of platelets. A sample of blood is drawn from a patients arm. A small amount of platelets in blood smears compared to the normal range of 150,000 to 450,000 platelets in microliter of blood suggest thrombocytopaenia, which is a common symptom in Epstein syndrome.A urine sample is often collected where a urinalysis can be used to determine the volume of proteins excreted in urine. Abnormal amounts of protein detected means the patient has proteinuria. Patients with Epstein syndrome often have large proteinuria where they excrete above 3.5g of protein in their urine in a day.
Other causes include:
Anxiety
Brain tumor
Chronic pains
Concussion – a mild traumatic brain injury
Diabetes
Fibromyalgia
Head injury
Hypercalcemia – too much calcium in the blood
Hypermagnesemia
Hyponatremia – low blood sodium
Hypothyroidism – the body doesnt produce enough hormones that control how cells use energy
Meningitis
Mood disorders – depression
Multiple sclerosis
Narcolepsy – disorder of the nervous system
Skull fractures
Sleeping sickness – caused by a specific parasite
Stress

Medicine
Analgesics – mostly prescribed or illicit opiates such as OxyContin or heroin
Anticonvulsants / antiepileptics – such as phenytoin (Dilantin), carbamazepine (Tegretol), Lyrica (Pregabalin) and Gabapentin
Antidepressants – for instance, sedating tricyclic antidepressants and mirtazapine. Somnolence is less common with SSRIs and SNRIs as well as MAOIs. Antihistamines – for instance, diphenhydramine (Benadryl, Nytol) and doxylamine (Unisom-2)
Antipsychotics – for example, Lurasidone (Latuda), thioridazine, quetiapine (Seroquel), olanzapine (Zyprexa), risperidone and ziprasidone (Geodon) but not haloperidol
Dopamine agonists used in the treatment of Parkinsons disease – e.g. pergolide, ropinirole and pramipexole. HIV medications – such as efavirenz
Hypertension medications – such as amlodipine
Hypnotics, or soporific drugs, commonly known as sleeping pills. Tranquilizers – such as zopiclone (Zimovane), or the benzodiazepines such as diazepam (Valium) or nitrazepam (Mogadon) and the barbiturates, such as amobarbital (Amytal) or secobarbital (Seconal)
Other agents impacting the central nervous system in sufficient or toxic doses

Assessment
Quantifying sleepiness requires a careful assessment. The diagnosis depends on two factors, namely chronicity and reversibility. Chronicity signifies that the patient, unlike healthy people, experiences persistent sleepiness, which does not pass. Reversibility stands for the fact that even if the individual goes to sleep, the sleepiness may not be completely gone after waking up.