You know how satyrs think of unseelie and seelie as sunshine and moonlight satyrs?
I think sluagh can be attic or basement. Seelie are the sort to drift about an attic filled with dusty and forgotten things, abandoned dreams, maybe standing on a balcony as storm rages, watching the weather with an overwhelming melancholy of what-might-have-been.... whereas unseelie are lurking underground, amidst the dank and unpleasant things, dwelling on things long past and perhaps seeking recompense from those who have wronged them, knowingly or not...