I think my dog is having seizures! Help?!?

She's a 10 yr old cairn terrier. Lately she has had the shakes. Like all the muscles in her body quiver. The shaking comes & goes. She also does this thing where she slings her head around & her tongue just flops around in her mouth. Her face muscles twitch uncontrollably also. Someone said that dog epilepsy can begin with the shaking & get worse. I'm not sure how true that is, but it seems like that's what's going on. Please help? She's been my best friend since I was five. I really want to do all I can to help her. <3