Oops, it doesn't look like 'serotonin day' is a national day..

Other days

pampering

Pampering Day
hot chocolate

Hot Chocolate Day
polyamory

Polyamory Day
lisp

Lisp Day
china

China Day
ask out your crush

Ask Out Your Crush Day
artists

Artists Day
first love

First Love Day
singles

Singles Day
ruby

Ruby Day