The medical drama’s upcoming festive instalment, titled All I Want For Christmas, will showcase the issues around hospital blood shortages.

Hudson, who will make a guest appearance in the special, previously had to receive around six pints of blood because of the condition in which the number of red blood cells or the amount of haemoglobin in red blood cells is less than normal.

Appearing on ITV’s Good Morning Britain, she said: “I just thought I wasn’t feeling great. It had been a while, a good couple of years, I just felt like things weren’t right and I thought ‘I’ve turned 40 – is it perimenopause or is life just too busy and I’m just not dealing with the daily stresses?’

“So I got an MOT at a medical centre and it turned out it was nothing to do with my hormones, it was actually down to the fact that I had chronic anaemia.

“So my HB (haemoglobin) levels were off the scale. So I was struggling breathing. It affected a lot of my body and my mind and everything. I had a couple of blood transfusions.”

The 41-year-old soap star, who is now on medication which she may be on forever, emphasised the importance of blood donation during the festive period as supplies can be low.

In the teaser trailer for the special, a voiceover can be heard saying “the hospital is on amber warning, blood supplies are low”.

The episode will feature testimonies from real-life contributors who have faced problems as a result of blood donation issues in the UK, as well as interviews with key workers in the NHS.

“Obviously it’s a brilliant drama but there’s a really good message behind it that actually people need to help a little bit more if they can”, Hudson said.

She added: “You don’t realise actually how much somebody’s blood supply could save a life. They say that a bag of blood can save three people’s lives.

“Especially this time of year, we’re low on blood donations and I think that’s because people are so busy.

“It’s Christmas, they’ve got other things going on, or there’s more accidents because of the weather, or we’re all rushing.”

The actress, known for her roles as Katy Harris in Coronation Street and Donna-Marie Quinn in Hollyoaks, said she would love the special to have a “happy ending” but teased that it will leave viewers wondering what happens.

The Casualty Christmas special will be on BBC iPlayer from 6am on Saturday December 21, and will air on BBC One at 9.20pm that night.