Post-holiday syndrome refers to the mood of melancholy and depression that many people feel after the Christmas, New Year celebrations and even after trips. In fact, this type of "syndrome" can be easily noticed in people who are always energetic and on the go but who now seem unusually tired and irritable. In this context, "syndrome" means a group of symptoms that occur together. Unfortunately, post-holiday syndrome is not a medical condition, but it is an actual experience.