Would love to know their source for this:

spell: (southern U.S.) a trance state in which individuals "communicate" with deceased relatives or with spirits.

In Kentucky, at least, a "spell" or a "sinkin' spell" meant nothing more than an intense bout of "feelin' poorly." Absolutely nothing to do with the supernatural. So far as I know this was the case in both black and white vernacular. Granted, Ky. is Mid- rather than Deep South, and it is the sort of thing I'd see them believing in, say, Alabama.

'Feeling poorly' or 'doing poorly' was the Irish Quebec vernacular for everything from deep depression to asthma. Bitty Dag was not at church because she was feeling poorly.

The wide distribution of this term makes me wonder if it started in Ireland.