Explain why excitement is described as appearing to be the opposite of stupor, yet the two often occur within the same underlying illnesses.

Excitement, markedly increased motor activity, and stupor, a profound reduction or absence of movement and responsiveness, sit at opposite ends of the same spectrum of disturbed motor activity, yet both can arise from the same underlying illnesses, such as catatonia or severe organic brain disease, sometimes even alternating within the same patient over time. This is because what unites them is not the direction of the disturbance but the fact that both represent a breakdown in the normal, moderated regulation of motor activity in response to the person's mental state and surroundings, with the illness able to push that regulation toward either extreme, excessive or absent activity, rather than excitement and stupor reflecting two fundamentally different disease processes.