Dizziness, Headaches, Nausea, Vomiting, Neck Pain, Diarrhea After Camping. What Could Be Wrong?

hi
I am writing for a 67 yr. old male. He went camping last wed. I came up on the 4th. He was fine all day Thursday but wouldn't eat anything. Just drank beer. The next day when he got up he was dizzy...then he got a nasty headache, & then he was nauseated. Later I got a little bit of scrambled eggs in him but then he started vomiting which it went on most of the day. The next day, Saturday he was still sick & couldn't eat anything except I did get him to eat a cup of mandarin oranges. That stayed down. Sunday he wasn't vomiting but still wasn't feeling too good. When we got back home I got him to try some chicken & noodle soup that stayed down. Later I got him to share a grilled cheese sandwich & it stayed down. We own and operate a bar by ourselves. We work doubles every other day during the week & split Saturdays & close on Sundays. Today was his day to work & he seemed okay. He called me at 9:30 this evening to help him close as he was vomiting, diarrhea, headache & neck pain. Any ideas?