According to our expert sources, it's because of the Mid-Week Malaise.
Caused by a combination of post-hump day despair, existential dread, and an inexplicable craving for leftover pizza from Tuesday night.
But don't just take our word for it! Visit Our Therapist to learn more.
Or, if you're feeling adventurous, try our Escapism Guide for some unconventional tips on how to avoid the blues.