Vix
You can sign yourself off for upto 7days its called "self certification" however if you are off more than 7 days your employer has a "right" to a Drs note explaining why
If they dont receive this they can discipline you
However if you have a history of lots of small days sickness they can clamp down
"most" employers allow 20 days a year before they get the arse
The 3days before sick pay is called "waiting days"
Nige