Here is the link to the POIS Wikipedia article. It gives good basic information about what POIS is:
https://en.wikipedia.org/wiki/Postorgasmic_illness_syndromeThere is a lot of useful information in that wikipedia article. For example, you will find in it the criteria created by Dr Waldinger to diagnose POIS:
https://en.wikipedia.org/wiki/Postorgasmic_illness_syndrome#Diagnosis Please also
note that on the left column, you have links to versions of this POIS Wikipedia article in several languages, like French, Spanish, Portuguese, Arabic, Chinese, and so on. However, they may be in various states of development, and not as complete in every language, and the content is not always the same neither.