seizure?

My cat had been lying around all day yesterday then when she got up she could barely move, she seemed to have very little control of her back legs.  We thought she may have been hit by a car so we took her to the vet.  The vet said she didn't have any signs of injury and he thought she had a calcium deficiency...she has 5-month-old kittens )which were born in the litter box).  She has the same look of shock that she had on her face then.  Dilated pupils and a blank stare at nothing.  Now that she's back home she is panting rapidly, arches her head back and her back legs are quivering.  Her front legs are like locked straight out and she seems to try to move but can't control her movements.  Any ideas?  I thing the vet missed something.

I think you need to get a second opinion.  

I am moving this to the Health forum so the folks there can see it.  

Please keep us updated! 

I can not say for certain what is going on but I would advise you to take her to another vet ASAP