Our fit and healthy 16-year-old son collapsed and died weeks before Christmas - 14 years on we still don't know exactly why it happened

The parents of a fit and healthy 16-year-old boy have revealed their confusion and pain after he collapsed and died suddenly on the floor with no explanation.Danny Nicholls was found lying next to the Christmas tree in the living room at his family home in Chorley, Lancashire, in December 2012 and later pronounced dead.Forensic pathologists later discovered he had suffered a sudden and unexplained seizure caused by the body's electrical impulses, which caused his heart to stop.His parents Eric and Lorraine Nicholls struggled to come to terms with Danny's death, especially considering he was a perfectly healthy boy apart from a recent cold.Mrs Nicholls saw Danny sleeping in bed when she left for work on the cold morning of December 10, leaving him undisturbed because he had a day off college.She gave her son a list of jobs to do but could not get through to him on the phone during the morning – and sent his sister Leanne to go and check on him.Leanne then called her to say she could see Danny on the floor in the lounge through the window outside. She dialled 999 and Mrs Nicholls raced home before running screaming into the house, but paramedics were already there and he was dead.Speaking in a new episode of Channel 5 documentary 'Cause of Death', Mrs Nicholls said she told her son: 'Daniel, wake up, it's mum, wake up'... and of course, he didn't.'She added: 'I'd gone out to work in the morning to a very happy, healthy 16-year-old still in bed. I've just got to understand why he just stopped breathing, just like that.' Danny Nicholls, who lived in Chorley, Lancashire, with his parents Eric and Lorraine Nicholls Danny's parents Eric and Lorraine Nicholls struggled to come to terms with their son's death Danny supported Blackburn Rovers FC, where his mother Lorraine worker as a tunnel stewardMr Nicholls also said: 'I came in, sat on the floor with him and I put his head on my lap and I think I was there... I think it was about an hour, just talking to him.' There was no sign of a break-in, no evidence of assault and nothing to suggest self-harm – so experts began searching for the unknown cause behind his death.The following May, a coroner in Preston recorded a verdict that Danny died from natural causes, but the exact reason for his death has remained a mystery.The programme sees forensic pathologist Dr Richard Shepherd, who has overseen more than 20,000 autopsies, reexamine the evidence behind Danny's death.He says: ‘When a seemingly healthy teenager collapses at home, we have to look really deeply and understand very clearly what has happened.‘Could this be a medical condition, could he have a congenital abnormality that caused his death, could he have some trauma, or could he have taken some substance that caused his death?’The documentary also hears from paramedic Gareth Barnes who was first on scene after the 999 call.He says: 'This was a 16-year-old, not responsive and I'm thinking 'what has caused this?' Is it a medical event, is it a traumatic event, is there any substances involved? Danny with his father Eric Nicholls, who spent an hour talking to her following his death Eric and Lorraine Nicholls visit Danny's grave during the new Channel 5 documentary Forensic pathologist Dr Richard Shepherd has reexamined the evidence behind Danny’s death'I can see Danny's sister Leanne is outside and she's very upset and distressed. Through the lounge window I can see Danny is on the floor, unresponsive. 'Myself and a passerby break the door down and I find Danny lying on the living room floor by the Christmas tree - and that's an image that I vividly remember and have remembered throughout these years.'Police found no evidence of any third party involvement in Danny's death, and pathologists concluded that there was no alcohol or drugs in his system.The teenager - a computer student at Runshaw College - was in very good health, had not been taking any medication and there were no previous causes for concern.But investigations found that Danny suffered a very unusual seizure caused by the body's electrical impulses, which stopped his heart beating.Pathology professor Timothy Dawson, who conducted the post-mortem examination, said he had only seen four such cases during his career of more than 20 years.Danny was a big fan of Blackburn Rovers FC, where his mother was well-known from her work as a player liaison and tunnel steward at Ewood Park.The former Southlands High School pupil was a mascot for the team aged nine, with player Robbie Savage once presenting him with his match shirt after a game.'Cause of Death' airs on Channel 5 at 9pm tonight