|Sleep dysfunction is also known as sleep disorder or somnipathy, it is a medical disorder. Sleep dysfunction effects normal physical, mental, social and emotional functioning of humans. This is normal disorder and usually temporary, may be caused due to stress or other factors. Sleep dysfunction is of many types which include dysomnias, parasomnias, circadian rhythm sleep disorders insomnia and sleep apnea. Review articles are the summary of current state of understanding on a particular research topic. They analyse or discuss research previously published by scientist and academicians rather than reporting novel research results. Review article comes in the form of systematic reviews and literature reviews and are a form of secondary literature. Systematic reviews determine an objective list of criteria, and find all previously published original research papers that meet the criteria. They then compare the results presented in these papers. Literature reviews, by contrast, provide a summary of what the authors believe are the best and most relevant prior publications. The concept of "review article" is separate from the concept of peer-reviewed literature. It is possible for a review to be peer-reviewed, and it is possible for a review to be non-peer-reviewed.