Hello and thank you for using this site to help you.
This breed of dog (what makes up this breed) is prone to disc issues. With that you are going to find a dog that is reluctant to move, will yelp if touched or picked up and often they seek a place where the owner will not try to get them from such as a closet or under a bed.
The fact that the dog is hiding and shivering tells me he is in pain.
Other causes for these actions would be something the dog ate that it should not have, such as fatty foods that would cause pancreatitis as this is very painful as well.
I would take the dogs vital signs, gum color , capillary refill time etc. to see if you have an emergency on your hands or if it can wait until tomorrow.
taking the vital signs: http://www.petplace.com/dogs/what-is-normal-in-dogs/page1.aspx
You can give aspirin to ease the pain. keep the dog on the floor or crated, no jumping or climbing up steps. Keep food and water close by.
Here is dosing for aspirin which should only be given if the dog is not on any other anti inflammatory drug (NSAIDS) and should only be given two days tops or ulcers can occur. http://www.petplace.com/article/drug-library/library/over-the-counter/acetylsalicylic-acid-aspirin
information on disc pain
lower spine http://www.petplace.com/dogs/intervertebral-disc-disease-thoracolumbar-area-in-dogs/page1.aspx
Picture of disc