Keeping calm under pressure is much easier said than done.
When you have been accused of something weather you did it or not. You WILL show signs of stress.
That is how a polygraph (lie detector) works, by picking up on the tiny signs of stress coursing through your body. Weather your telling the truth or lying through your teeth your body WILL show signs of stress.
Lie detectors are not allowed to be used or to provide evidence in the British legal system. one reason for that is they have been found to not always tell the truth (not a 100% accurate) and in the USA you bet that many people have wrongly gone to jail based on a polygraph result.
So just imagine your sat in front of an investigation officer at work who you have never met before but has a folder containing allegations about you..... The investigation officer is naturally going to see the signs of stress and assume your lying and what a good job they are doing. the mare fact that they invented a machine to test if people are lying means it is almost impossible for an untrained person to tell if someone they have never met is telling the truth or telling a lie.
Tip of the week:
It is not going to harm your defense if you used terms like (I am feeling very stressed at the moment and i would like to take a few minutes to compose yourself) They will have to concede to your request, as deliberately putting someone in a stressful position and then questioning them can be seen as torture.
If they refuse your request tell them you will be calling P4p.