Can somebody please help me about my cat ? :(?

I don't know what's going on with my cat! :( i got her when she was about 2 months old, she's currently 6 months, she hasnt had her shots because a friend just gave her to us after and we dont have the money. she seems fine mostly, but lately she;s been scaring me with these spazz out moments. she's fine then next thing i know shes like falling off the counter biting like hell at her leg or something, i dont think its a seizure, she snaps out of it when i pick her up and wiggle her a bit. and shes fine, but she has them atleast once or twice a day.. i just worry cause she loses clumps of hair sometimes from biting so hard.. she still eats and drinks just fine. and i recently put flea stuff (seargants for cats and kittens) because i thought it might be fleas but she just did that again...im at a loss...what are these? please help. thanks