Sudden loss in leg strength

[McDonalds24]

I have a 7 year old short legged 'JRT' named Ricky, hes always been a healthy and happy pooch running around jumping on things and causing a little mischief. All seemed normal until Tuesday morning (11/19/13) when he seemed to lose the strength in his legs that allowed him to jump up onto the couch, bed or chair.  He has little trouble going down the stairs but now has trouble going up as he takes one step at a time, compared to how he usually bolts up and down the stairs and gets around, this is really concerning.  His personality seems the same but I have noticed he seems to be eating less this week.  My mother said he fell out of the bed Monday night and yelped which could have something to do with it.  I want to take him to the vet asap but my parents are putting that off until next Monday...

I was hoping someone on here may have some idea what happened to him or any advice?

[McDonalds24]

Like I said he cannot jump or get up on things on his own, to sit with us on the couch or bed he must be lifted. He can handle the stairs on his own, though gingerly,  I am to poor to take him to the vet on my own, and my parents are ignorant and believe it was a spider bite and will take care of itself
(prolly to avoid a vet bill). As an added note he pulls his front paws back when I go to feel them.

[RICK2990]

TAKE TO THE VET AS SOON AS YOU CAN,,,, FOR NOW RESTRICT HIS ACTIVITIES, NO JUMPING  NO RUNNING  NO STEPS NO JUMPING ON AND OFF FURNITURE, THESE ACTIVITIES MUST STOP, UNTIL SEEN BY THE VET. NOT SURE WHY HE WOULD EAT LESS