Why do I always get sick when I take time off?

You've planned some time off. You madly finish off all the work you need to get done before your break. Your first day of leave begins and... you get sick."Leisure sickness" is a term coined by Dutch researchers for people who are more likely to get sick on the weekend or holidays than during the working week.There's very little science to back it up, but there are some theories as to why it might happen — and what you can do to avoid it.