Alcohol and lack of sleep will do it for sure.
This is a lie.
I'm citing personal experience.
A few weekends ago I got extremely intoxicated, stayed up the entire night because I was with a girl (same girl who told my roommate she wouldn't talk to me because I was too intoxicated) then in the morning drove her back to her school, got lost on the way back, finally got back to mine, etc. (Point is that I had to actually do stuff the next day, not just lay around) Anyway, I didn't get sick. Alcohol and lack of sleep definitely isn't a "sure" way to get sick. Similar situation on different weekends, too.