My mom, born in 1922, had a friend named Katie since kindergarten. Katie comes from Detroit, and now lives in central Michigan. Anyhow, Katies's the kind of person who would use the term "sesh." She would visit my folks in "Sara," not Sarasota (Florida), and then she'd take a side trip over to "Miam" (Miami). I'm not sure where and when Katie picked this up,   but my dad has been talking about this trait of Katie's for years.
I think it's kind of a 1940's "cool" thing or something.
Maybe it's what octogenarians do for a good time - abbreviate words...

-Joe-