She suffers from two neurological disorders- Narcolepsy and Cataplexy. Both conditions are capable of causing a temporary loss of consciousness.
Cataplexy causes an abrupt loss of voluntary muscle tone--as severe as total physical collapse and it may be triggered by strong emotions like laughter while narcolepsy results in excessive daytime sleepiness.
As a result of the disorders, Dawn's often in the hospital with head injuries and is forced to take several medicines daily to stabilise her condition.
She told the Sunday People: 'Every time I laugh hard or get upset, I collapse and my head falls forward like a rag doll's.'
She said, 'I watch the DVD and rewind it every five minutes once I recover.'
'I've had to learn to hold back my emotions. Some days I can laugh more than others, but it's changed my whole life.'
She even collapsed on her first date with now-husband Rhys, 42, after he told her a joke and she burst into laughter then fell and hit her head on a table at her daughter Amy's 16th birthday.
Having narcolepsy also means Dawn is unable to stay awake some mornings to take her five-year-old son Sam to school.
At weekends Dawn stops taking her medication to give her liver and kidneys a rest and relies on her husband Rhys to look after her.
She told the People: 'I can't even shower without Rhys being there to make sure I don't pass out. It's robbed me of my dignity.'
If he knows she is going to laugh, he has to make sure she is prepared.
She said: 'Rhys wanted to show me a funny clip on YouTube while I was eating. He told me to put my knife and fork down and finish my mouthful. Then he played me the video and of course I collapsed.
'I would sell my kidney for a cure, I'm so desperate. I feel like I've had half of my life stolen but I try not to dwell on it too much as it makes me cry.'