It's National Hangover Day on January 1st.
More on Hangover Day and the other days on the 1st below.
The day shown for 'National Hangover Day' is shown as we detected that day mentioned the most out of all the references to national days there were on January the 1st across social media. Our algorithms examine all of the references to National Days across social media and updates whatnationaldayisit.com hourly, with our homepage displaying the current national day. This crowdsourcing of data method to assess the National Day date is used as opposed to being connected with any Government sacntioned lists :D Hurrah for democracy by concensus!