Mother-of-three has rare condition which means she can't stand up for more than a MINUTE without fainting Kathryn Marshall got Postural Tachycardia Syndrome after a car crash Condition means her heart rate rockets every time she stands up and blood flow to her brain is restricted - this causes light headedness and fainting She can't stand up for more than a minute at a time and passes out every time she stands in a shop queue, or walks her children to school She is always covered in cuts and bruises caused by her constant falls A mother-of-three is unable to stand up for more than a minute without fainting because of a rare condition. Kathryn Marshall was involved in a car accident two years ago after which she began to suffer from bouts of dizziness and fainting. The condition made her pass out every time she queued at the shops or walked her children to school - she couldn't even hug her children without risking collapse. Kathryn Marshall, 38, has a rare condition which means she faints if she stands up for more than a minute. She says she just want to be a 'proper mummy' to Harry, 8, (far left), Erin, 6, (left) and Chloe, 10, (right) After a string of tests and medical examinations baffled doctors finally diagnosed the 38-year-old with Postural Tachycardia Syndrome (PoTS). The rare condition causes her heart rate to shoot up when moving from a sitting to standing position, leaving her with extreme feelings of light headedness and restricting blood flow to her brain. The rare condition has made her life increasingly difficult as she longs to be a "proper mummy" to her children and live a "normal family life," but cannot get up from the sofa. Mrs Marshall, from Swansea, said: "All of the things I used to take for granted, I now have no control over. And it is the little things that I miss the most. I can't play with my kids like I want to, I can't even make it up the stairs without having to sit down half way. The guilt I experienced from not being able to be a proper mummy to my three little ones was terrible. Mrs Marshall (pictured on holiday with her children and husband, Chris, before her illness) has Postural Tachycardia Syndrome which causes her heart rate to rocket when she stands up Mrs Marshall (pictured with daughter Chloe) developed the rare condition after being involved in a car crash two years ago. She spent four weeks in hospital before being diagnosed After being diagnosed, Mrs Marshall had to give up her job as a nurse and solely relied on husband Chris, 41, to run the family home. Simple tasks such as doing the washing up are now almost impossible for her. She has suffered a series of dramatic falls in public and at home - and is constantly covered in bruises and cuts from her falls. But she is determined to push on to give her three children - Chloe, ten, Harry, eight, and Erin, six - the chance to go to the park or on a family holiday. Mrs Marshall said: "There are so many things that they want to do and I want to do with them. The condition means Mrs Marshall is constantly falling over so she is always covered in cuts and bruises Mrs Marshall faints every time she stands in a queue or walks her children to school. She has even fallen down a flight of stairs after collapsing But I know that it will just wear me out and make me feel ten times worse if I do. It's very confusing and upsetting for the children - they beg me to play with them, they say "please mummy." It just breaks my heart to have to say no to them. I feel like they are missing out on so much and it's all down to me. Mrs Marshall was involved in a car crash in March 2011 which left her with a whiplash injury to her neck. In the weeks after she started to have palpitations and to become breathless - symptoms she blamed on the stress of the accident and looking after three children. But six weeks later she collapsed and spent four weeks in hospital and, after thorough testing, was diagnosed with PoTS. Mrs Marshall has to take 12 tablets every day to keep her symptoms at bay, to lower her heart rate and blood pressure and to prevent her from fainting Mrs Marshall: 'When I was first diagnosed everything was very bleak. No one knew what was wrong with me - it was terrifying The young mother has to take 12 tablets every day to keep her symptoms at bay, to lower her heart rate and blood pressure and to prevent her from fainting. Mrs Marshall has also sustained a number of serious injuries after collapsing unexpectedly, including falling down a flight of stairs which left her battered and bruised. She added: "When I was first diagnosed everything was very bleak. No one knew what was wrong with me - it was terrifying. But I have just had to learn how to live my life in a different way. On the outside I look completely normal. Mrs Marshall said: 'There are so many things that they want to do and I want to do with them. It breaks my heart to say no to them. I feel like they are missing out on so much and it's all down to me' Mrs Marshall said: 'When I was first diagnosed everything was very bleak. But I have just had to learn how to live my life in a different way I put on a smile and do my hair and make-up. But it is hidden deep within me - it is a hidden disability. I just try to think positively and I am very determined. I will beat it. Mrs Marshall has now returned to her job at a general practitioner clinic and taken up two days as a nurse. She said: "Fortunately it's sitting down so I can carry on working without worrying about my condition." PoTS is an abnormal response by the nervous system to standing up. It causes an increase in heart rate and altered blood supply to the brain. This causes dizziness, fainting, tiredness and palpitations. Other symptoms of PoTS include shakiness, shortness of breath, chest pain, headaches and stomach problems. Some patients find the condition very disabling while others have mild symptoms and get better without any treatment. The condition can be triggered by an illness, pregnancy, trauma and immunisations. It can also occur in teenagers who experience a sudden growth spurt. In some cases the condition results from another illness such as diabetes, MS or Lyme disease. Source: PoTS UK