A mum-of-three was left heartbroken when her healthy son died shortly before his second birthday with no explanation.
Hannah Johnston and her husband Keith grew into a family-of-five as they welcomed their third child, William, into the world in 2020.
William was healthy and behaving completely normally when suddenly, in November 2021, he suffered a seizure followed by two cardiac arrests, and ultimately passed away.
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"I text my friend at 4.42pm about the fact our kids were having their dinner and two minutes later I called 999. That's how quickly our life changed," Hannah told the Mail Online.
Paramedics arrived at the home and it was determined that William had suffered a febrile seizure; a fit that can happen when a child has a fever, the NHS explains.
The seizure terminated after 45 minutes and Hannah was allowed to touch her youngest son, but he was 'not responding'.
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William was taken to an ambulance outside the home, and about 10 minutes later a paramedic informed the parents that the young boy had just suffered a cardiac arrest.
He suffered another while on route to the hospital, and once there doctors worked to make him stable again.
William underwent an EEG to record his brain activity and it was then his parents learned their child's injuries were 'catastrophic and irreversible'.
William passed away on 17 November, 2021, when he was just 21 months old.
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His death has been attributed to Sudden Unexplained Death in Childhood (SUDC), the sudden and unexpected death of a child between one and 18 years old, which remains unexplained even after a thorough investigation is conducted.
Hannah hadn't previously heard of SUDC, but she's now working to raise awareness of the phenomenon.
Speaking to TYLA, Hannah explained: "Awareness is needed within the medical sector and the public. I want research to be carried out and for SUDC to be predictable and preventable.
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"We need to educate doctors on this and request time be dedicated to finding a cause of SUDC."
The mother described losing a child as 'the most horrific thing' to ever happen to a family, but told BBC News the added layer of not having an explanation for William's death forced to think about 'what [she'd] missed'.
"There were just no answers as to why this happened to him," she said.
As part of her efforts to raise awareness, Hannah joined other parents and activists at Westminster as the issue was debated for the first time in Parliament this month.
Emily Brown