Becky Usher, 38, first developed a high temperature and a sore throat on Sunday afternoon.
She experienced breathing difficulties at her home in Heckmondwike on Tuesday and began to slur her words, so her concerned partner called 111.
Becky, who has a six-year-old daughter, was rushed to Pinderfields Hospital where she was immediately admitted to intensive care after her condition worsened.
Her family say she has tested positive for coronavirus and remains in the intensive care unit, where she is in an induced coma and relying on a ventilator.
Becky, who works as a nurse at Dewsbury and District Hospital, has a number of underlying health conditions including Long QT syndrome, a hereditary heart condition which left her fighting for her life in 2004 after having multiple heart attacks.
Her sister Kelly Ann Cardwell, 42, described the family's heartbreak as they are unable to be by her side in hospital, where she remains in a critical but stable condition.
Kelly said: "The hardest part is not being able to see her and not being able to see my parents, thinking we may not ever see her again.
"Becky almost died in 2004, she collapsed outside my house and had to be resuscitated in hospital having suffered a number of heart attacks.
"It just seems such an injustice for her to have fought so hard in 2004 and have a second chance, just to be fighting again now with none of us by her side."
Becky's close friend, who runs Facebook page Take Ten, posted a heartwarming message urging others to send in their words of support.
Hundreds of people have commented on the post, praising Becky for putting her life on the line to help others.
Kelly said: "Becky has basically risked her own health for others.
"For the other NHS angels and key workers supporting everyone through this worrying and difficult time, we can't thank you enough for the risk you are taking to save other's lives.
"Just know how much everyone truly appreciates the sacrifice you are making each day."
Kelly has posted a handmade card with a big red heart inside to Pinderfields, urging her sister to 'keep fighting'.
She added: "Becky is bubbly, outgoing and has a heart of gold. She is also very stubborn and a real fighter.
"Please - our sister, youngest daughter and beautiful mother to Ellie - fight this with everything you have like you did back in 2004.
"We know you can beat this and you have so many people waiting for you to get better and make more memories with."
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