However, this is not usually a reason to stay at home, or leave work halfway through the day.
However, one of our client's employees did claim to have such a stomach ache that it was impossible for him to work - and he went home and stayed at home.
We would not normally be called in to investigate such a claim, but on this occasion we were, because it gave rise to rumours that the man was working outside our client's company.
The first time we kept the man under surveillance, our investigators saw him doing errands such as picking up heavy items. The second time he was under surveillance, it was clear that he was working for a company other than our client's.
It was whilst our investigators were carrying out this observation that fresh rumours began to circulate in our client's company - that the man had taken company goods.
Our investigators interviewed this man and confronted him with their observations. He admitted that he had a second job. And the goods he had taken? He said that part of what he had taken was, in his opinion, waste material and for the rest he had written a ticket.
He had simply not handed in this ticket: it lay in his material cupboard. He said that his stomach ache had gone and he could have returned to work earlier, but decided to wait until Monday to be absolutely sure that he was fully fit.
He could well have had a stomach ache due to what followed next - he was fired.
One of our investigators accompanied him to his workstation. There the man took a book of tickets out of his cupboard and began to write. He tore a ticket out of the book and handed it to our investigator. Written on the ticket was a list of the goods he had taken. He said that he had forgot to write the ticket out previously, and asked if our investigator give this ticket to the company director.
Once again, an investigation showed rumours based on fact. Often directors and managers allow rumours to go unheeded and their truth is only discovered after much damage has been done. Prompt reaction to rumours can save management a lot of stomach aches.