May blues isn't an actual disease, it's a feeling you get when you've been on break and don't want to go back to work. The equivalent American term is post-vacation blues.
Edit: And that's pointed out in the next comic. Dang it.
Hatsuyuki explained it.I've just got no motivation...Ach, I wonder if they're all...right...It appears that Roma-san and Littorio-san are off sick.Is what she said.That's us to a T.This is, what was it... May Blues, apparently.Due to May BluesSurely that's from the May Blues, no?Reason - DetailsManmenmi!Transliteration of the girl Inkling's "voice"The May Blues is a terrifying disease, endemic to Japan.Nee-san, I've come all over with a terrible feeling.I know! Me neither!Mei=Blews?As an aside, I have been suffering from this illness for an extended time.Its symptoms include drowsiness and a sense of fatigue; but its main effect is a complete loss of will to go out on missions.
