You've struggled through the week, meeting impossible deadlines, and now is your chance to relax.
But what happens? You realise you're not only tired, but ill. The cold you've been warding off for days grabs you by the throat and the weekend passes in a haze of paracetemol. It's as if you've given yourself permission to be ill.
Can we really affect the onset of illness like this? Research in the past ten years has shown that there are indeed chemical links between the brain, the nervous system and the immune system, but exactly how it all fits together is unknown.