What is Roderick's malady?

Poe never really tells us what Roderick's malady is. Like the house of Usher, Roderick seems to be disintegrating, “A cadaverousness of complexion; an eye large, liquid, and luminous beyond comparison ; lips somewhat thin and very pallid....." Roderick's emotional state is fragile too, "and I soon found this to arise from a series of feeble and futile struggles to overcome an habitual trepidancy - an excessive nervous agitation..." Roderick is very much a part of everything about Usher that is crumbling including his "dead" sister.