It is National Hide Under the Bed Day, a holiday inspired by sick cats.
What? You say you haven't ever had a sick cat, let alone one that was worthy of inspiring a national day of hiding? Well let me share with you the origins and benefits of this day.
When a cat is sick, hurt, wounded, or otherwise feeling craptastic, it finds a dark, cave-like environment in which to crawl. Under the bed, in a box or paperbag, into your luggage...all of these are worthy contenders in the cat's mind.
The cat stays here, growling and howling, until A) it feels better, or B) you haul it out and stuff it into a cat carry-all and bring it to the vet, or C) it casts off its mortal coil and heads for kitty heaven.
(Note: Option B is very, very dangerous and will result in the shredding of your unprotected hands. I recommend the donning of oyster shucking gloves prior to extracting your sick feline from its cave-like hidey-hole.)
So, those are the origins. Now, for the benefits.
On NHUBD, you can wake up, not go to work, and find someplace warm, dark, and comforting to spend the rest of the day. No one will bother you, no one will ask anything of you. The world is, essentially, not there for the day.