case of the Mondays

noun1

1. •
   (humorous) An instance of "the Mondays", a fictitious disorder associated with the tiredness, irritability, or distractedness that comes from returning to work after the weekend.

   • A reporter, who has worked his way up to a top-level and high pressured position with a large metropolitan daily, suffers from a chronic case of "the Mondays." — 1975