I think my cat is having seizures?

my cat had a small shelf fall on him and we thouhgt he was fine .a few weeks later he was having what i think are seizures. the symptons are as follows he meows harshly and starts sckracthing himself uncintrollably when hes done he cant move andsits ina wierd position somtimes all the other cats come running when they hear this . it only hapens when he is moving or scrathing violently. it also hapens in cylcles like a few a week too one every 6months pelaes help