My 2 1/2 yr old chi-llhasa has suddenly become sick with something. He doesnt want to run around, drink, eat. He just wants to lay on his back with his bottom legs open which seem very stiff. when he lays with them closed, his legs twitch a lot.   What could this be from? He is an indoor/outdoor dog.

Optional Information:
Age: 2; Male; Breed: Chi-Llhasa

Already Tried:
Cuddling, warm blankets, petting, rubbing Pets legs.