Sex is supposed to be fun and make you feel amazing, right? But according to a new study, a third of women experience "post-sex blues." The study, conducted by Australian researchers, showed that a third of the 200 women surveyed admitted experiencing sadness, anxiety, irritability and restlessness after sex. 10 per cent said they frequently or almost always feel sad after sex. Robert Schweitzer, the study's author, says there's no clear reason for the feelings of sadness.