My mini-pom is having health issues...?

My dog has some kind of seizures/spasm. She can be fine one moment and then she will stop and lie down and then her legs will contract (bend) in, and her head will curl in to the right or left. Her body will tense up and she shakes some and once in a while whimpers. She doesn't walk or move when this happens. This has been happening about six months now, but it did stop for about a month and has just started up again. In general though, she is in good health. She eats, plays, goes potty. She is a mini Pomeranian, 5 years old. Any clues??