my elder twin daughter is 9 months old.from the past 10 to 15 days she is getting excited at times n is acting very strange.she is making her fists stiff,her entire body stiff,biting her mandibles,she makes her neck stiff too...for a few seconds and then continues her noramal behaviour.from the past 2 days she is doing it repeatedly,like around 7 to 8 times within a minute and then it varies in time .she doesnt do it iin her sleep,but only when she is awake,is playing or sitting.could you please suggest me what could it be and what precautions can i take to prevent that.