What's wrong??

I have a 5 year old chihuahua who has been having seizures, 3 that I know of in the span of a month, and I don't know why! I am taking her to the vet Friday but I am worried sick about her.. She has never had a siezure up until the first one about a month ago, when she has them it seems like a few minutes before she had either been accidentally ran into or jumped off the couch and landed wrong which I feel really horrible about but accidents happen. I don't know if being accidentally bumped could cause them or if it is just a coincidence, I've never had a dog do this before. Anyways, they only last 3 or 4 minutes, she can't walk on her left legs and gets all shaky, and afterwards she is perfectly fine, she does NOT drool or pee or anything like that. They seem very small and I don't think she knows she's having them. A little info on her, she just turned 5 this year, she has NEVER had any health issues, illness, or anything, she has always been a picture of health. She has had two litters of puppies, the first a couple years ago, and the second in May. Everything went smoothly, no complications, natural birth. She doesn't seem to have anything else wrong with her, although over the past few months she's gotten fatter, not really fat by any means, but for her it is because she's always been skinny with a stomach that curves up and now she's filled out, which to me and anyone else who has seen her on a regular basis over the years, makes her look fat. I don't know why she's gained weight, I haven't fed her more than usual. So not sure if it's connected to the siezures. Anyways I'm looking for advice or someone who may know what's cuasing these or has had experiences like this themselves, please tell me anything you know!
Thanks.

I just saw this thread, and want to apologize for my belated response.  The beloved dog I had when I was young had seizures (only two, but they were severe and scary).  However, we never got a definitive answer as to what caused them.  How is your dog doing now and what did the vet say?  I hope your girl is okay.