What is wrong with my dog?

i have a chihuahua mix and she's about 9 years old. the past 2 days she's been acting weird...she hides all the time and when she walks, she walks really slow and wobbles. she has her tail down and ears back. she always lays down like she can't walk. when i put her outside she won't go. she eats though. i don't know what to do. i feel bad. we might take her to a vet tomorrow. does anyone recognize these symptoms?