from OED online: (check out the citations, esp. the 1st)

/ˈwuːfɪts/
Etymology: Origin unknown.
slang.

An unwell feeling, esp. in the head; moody depression.

1918 J. M. Grider War Birds (1927) 96 Curtis says he is suffering from the Woofits, that dread disease that comes from overeating and underdrinking*. [EA]
1918 J. M. Grider War Birds (1927) 207, I drank too much coffee before getting up and I'm as nervous as a kitten now. Must be getting the Woofits.
1932 Amer. Speech 7 338 [Johns Hopkins jargon.] Woofits, ailment that comes with ‘the morning after the night before’.
1958 ‘N. Shute’ Rainbow & Rose 100 Getting the woofits now, because I don't sleep so good.

*the quote appears to be accurate. link