Image copyright Amy Image caption Amy used to call in sick because of stress

Amy says she used to need to "pull sickies" once every couple of months because she couldn't face going into work.

"I'd have a few days prior arguing with myself to get up, and go in," she tells the BBC.

But recently she realised she was doing this because of her mental health issues, so now she calls in sick and says she needs to take "a mental health day".

"It is what I need - a day off to sleep, and rest and re-set. I'm twice as productive as I would have been if I take the mental health day rather than working through it. That tends to lead to burn out and utter exhaustion for me."

Almost half of Britons say they would fake a sick day - but the reasons for doing so are often more complex than they first seem.

Image copyright Getty Images Image caption Some say calling in sick allows them to rest and reset

Last year 15.4 million days were lost to work-related stress, according to the national Health and Safety Executive.

It is most often due to people being overloaded with work, but also down to having a bad relationship with your line manager.

One man, who prefers not to be named, told the BBC he pulls sickies because of the anti social hours has been forced to work. An oil and gas service technician, he is expected to be on call at most times.

But this means he is usually "offshore" for at least 20 days every month and that - despite claims to the contrary - his firm does not care about its workers or their families.

"They even ask us to cancel holidays or shorten them to cover jobs and we always work over Christmas," he said. "I've missed my children growing up, birthdays, special occasions - so I feel justified pulling a sickie now and again."

Image copyright Getty Images

The average worker takes around four sick days a year, according to the Office for National Statistics, although it doesn't monitor how many days are faked.

However, according to separate research from the Chartered Institute of Personnel and Development (CIPD), the figure has actually been falling, reaching a two-decade-low this year.

It blames the rise of "unhealthy" working practices such as presenteeism, whereby staff feel they need to show up even when they aren't feeling up to it.

"Organisations - particularly in the public sector - have also been taking a tougher line on absence over the last decade. But they are also doing more to support people who feel unwell," says Rachel Suff, senior policy adviser at the CIPD.

Often the problem is that people do not feel able to talk to their employers about still-taboo issues such as stress. This is despite the fact that there is no legal difference between taking a mental health sick day and a day off for a physical problem like a back problem.

"Depression, anxiety and other conditions can trap you in your house and make it feel impossible to face work, but it is far easier to tell your boss you're not feeling well, especially if you think your boss/your company will be unsympathetic," reader Evie told the BBC.

Image copyright Getty Images Image caption Workplace stress is becoming more of a problem

Hayley Lewis, an occupational psychologist, told the BBC that managers needed to focus on what was causing stress and unhappiness in the first place.

"It's often more about your relationship with your line manager. And if you're not getting on with them and you can't solve the problem it's sometimes easier just to pull a sickie.

"Also, in sectors where jobs have been cut, people are facing increased strain in their roles. When people don't feel secure in their jobs and have higher workloads they feel vulnerable.

"People want to be seen to be strong, so sometimes the easiest thing to do is to throw a sickie when it gets too much."

Of course, many take sick days because of physical as opposed to mental ailments. But in jobs where teams are under strain, some workers find it hard to justify doing so.

Chris, a former teacher, told the BBC that due to staff shortages at his old job, "if you were off sick it was even worse for the rest of the staff, and there was a lot of anger when you returned to work for having let down your colleagues".

Most organisations have systems in place to manage absence, says the CIPD. This might include a "trigger system", where managers are alerted when someone exceeds a certain number of sick days.

More controversially, some employers combine this with back-to-work interviews when people have been off - even for one day.

'People need support'

"It is the message that goes along with it that counts," says Ms Lewis. "Do people feel like it's the Spanish inquisition and they are being interrogated? Or is it done in the spirit of genuinely trying to find out what is going on. It differs from company to company."

The CIPD's Ms Suff says good employers show flexibility, and will give staff days off for bereavements and access to counselling when they are struggling with stress or other issues.

She says flexible working patterns - along with part time options for those who might need them - are also ways to keep your employees happy and absenteeism under control.

"It should be about supporting people when they are genuinely ill… but also encouraging genuine reporting around absence," Ms Suff says. "People will usually only take non-genuine sick days when they feel they can't share the reason."