German to English Medical Medical (general) psychiatric/physical eval

This is a doctor's evaluation of a mystic (Therese of Konnersreuth) in the early 20th century. The use of "Sitz" here baffles me. It has nothing to do with sitting, chairs, or the location of an institution:

Daß die Lähmung der Therese eine ausgesprochen hysterische war, geht aus der Art der Entstehung, dem Sitz und der Ausbreitung der Störung ganz unzweifelhaft hervor.

My draft:
That Theresa's paralysis was markedly hysterical emerges logically from its etiology, the setting, and the extent of the disorder.

If this is a stupid question, I will change it to "non-pro." :-)

Thanks!