Neurological issues in a small dog

Our dog is experiencing neurological issues that our vet is aware of but they have gotten worse lately so we are going to take him in. Although he's not in pain it's a bit worrying.

Joeybear just turned 12 at the end of last month. He's a Yorkie or Silky Terrier. He started having some occasional issues with shaking and eye movement in 2005, like one every other month, and slowly increased. We are now at several times a day. (It increased over the past 6 months.)

He shakes and his eyes blink. He'll start leaning forward towards the ground, but not fall over, and recently his back end has started leaning to one side (like the leg in that direction gave out.) He's been getting a little more tired over the year and thought it might be because he's getting older, but now I'm wondering if it isn't part of this. He also gets a little absent (the way he acts there is just "is anyone home?") sometimes, but like the tired I thought it might be due to age.

I know he's not having seizures and I've done research. I'm scared, prepped my dad, did my homework and now we'll have to wait for a diagnosis of some sort.