A teenager kissed his mum goodnight – and was found dead in bed next morning from a mystery heart problem.
Schoolboy Matthew Hughes, 17, had not complained of feeling ill.
A post-mortem failed to find a cause of his death.
Dad, Paul, 47, of Cardiff, said: "It could be six months or a year until we found out or we might never know."
An inquest was adjourned for more tests.
Matthew's funeral was held yesterday.
Paul, wife Fay, 48, and daughter Georgina are asking for donations to Sudden Adult Death Syndrome charity CRY.
