Amelia Logan, 26, was found dead in her bed by her mother, also Amelia, on Monday at the family home.
The mother-of-three dialled 999, but sadly it was too late to save her. Amelia, who would have been 27 on December 22, was due to see a hospital specialist the following day.
Grief-stricken Amelia says she can't understand why her daughter wasn't given a brain scan at Glasgow's Southern General, after other tests proved inconclusive.
She says doctors told her to video her daughter having a seizure. The post mortem did not shed any light on Amelia's condition.
Amelia, who works as a care assistant, said: "I always said, the worst thing that could happen to me would be to lose a child.
"It's a mother's worst nightmare come true.
"I don't understand why she wasn't given a brain scan. They always said, 'we will do this test first'.
Amelia's brother Thomas, 29, said: "It's so hard. It's the shock and the not knowing.
"There are so many things she never got the chance to do."
Amelia began suffering fits two years ago, forcing her to give up work as a hotel receptionist.
Epilepsy was ruled out and she was sent home with medication to try to stop the fits happening.
At one point she suffered three in one week.
Amelia, who was a doting aunty to three-year-old Shawn, and one-year-old Lexie and Cooper, suffered a fit on Friday, November 29, but had been well over the weekend. The night before her death on December 1, she was telling her brother Thomas about her plans to re-decorate her bedroom.
Amelia said: "The dog used to bark every time she took a fit.
"Amelia was in bed and I heard the dog barking after 1pm but when I went in she was lying watching TV.
"I got up at 8.30am on Sunday. The TV was still on. She was gone.
"I ran back to get Andy and phone for an ambulance but it was too late.
The family, who live in Milton of Campsie, are facing not only the heartbreak of Christmas Day but Amelia's birthday on December 22.
A spokeswoman for NHS Greater Glasgow and Clyde said: "Our thoughts are with the family at this very sad time.
"We would be happy to meet with Amelia's family to reassure them about the range of tests which we provided and to answer any questions about her treatment."