my 21 month old son has been waking up lately 2 or 3 times a night and he just screams and throws his body around, mostly his arms and head, and its like he is not even awake. he will fall asleep again in a moment just as quick as it started but the episodes last about 5 minutes. they have gotten worse since this tuesday when he had surgery, a hypospadious repair, but it started a while before that, does anyone know what this could be or what could cause it?