It isn't a constant thing but seems to come and go. Symptoms include a headache, horrible stomach ache, feeling sick and hot and just generally crappy. But it comes for an hour or so and you feel awful and then it goes and comes back a few hours later.
Everyone at work seems to be ill so whether or not it's just fighting itself off it's horrible. Nothing to miss work for but when it hits again you can't do any work as you feel so hot and ill. Fresh air seems to help.