The causes of this disorder are numerous and complex. If you're new to the profession, it's partly prompted by the fact that the school where you had your interview has been removed and replaced in exactly the same location by another. It looks the same, but its population has been swapped with hostile clones. The happy, clean, polite pupils are now a snarling satanic horde. The welcoming, supportive staff have metamorphosed into dejected, semi-conscious zombies.
If you've been in the same school for some time, you'll understand the causes. In the space of two months since the start of the academic year, Year 7 has managed to form terrorist cells and launch their first attack. It feels like the older pupils have taken them to their secret training grounds and, within 10 minutes, taught them how to change from highly qualified, skilled and intelligent human beings into screaming lunatics. Their weapons are simple: paper pellet, ink cartridge and the never-ending array of psychological torture, which ranges from humming to instinctively knowing when the request for a pencil will turn you into Attila the Hun.
Yet it's not just behaviour that causes the blues. For example, at this time of year, the sun only rises for teachers at the weekend. For the rest of the week, we travel to work in the dark and we leave in the dark - who has time to look out of the window in between?
Then there's the phenomenon of marking. No matter how many times you mark a set of books, they always need re-marking. Then there's the invisible set of books that no matter how many times you check always manages to escape the red pen. Finally, there's the sofa narcolepsy. What teacher can sit on a sofa for longer than 10 minutes without nodding off?
But the blues will end and that ever distant and fabled Christmas holiday will come, and with it that sherry-fuelled bacchanalia we call the "Christmas do". But a word of caution: so joyous are we that the evil beast called autumn term is dead, we can be tempted to over-celebrate. Remember, telling that member of staff what you really think of them, or finding alternative uses for the photocopy room, can lead to the January blues.
Greg Bellmore is the co-ordinator for gifted and talented pupils at Castle Vale school and specialist performing arts college, Birmingham