The 29-year-old won women’s skeleton gold four years ago in Sochi and triumphed again at the Olympic Sliding Centre in PyeongChang, peaking at the right time after a turbulent season.
“After the first run yesterday I was almost at the point of pulling out. My chest infection was stopping me from breathing,” said Yarnold.
“I just tried to get the second run down and then fight another day today.
“If it wasn’t for my physio Louise Turner telling me to go down again, I’m not sure I would be here today.
“The emotions are gratitude to the whole team to get here, and relief, and exhaustion. And lots of crying.”
Yarnold was joined on the podium by team-mate Laura Deas, who claimed bronze behind silver medallist Jacqueline Loelling of Germany after Austria’s Janine Flock slipped from first to fourth on the final run.
It is the first time Britain have won two medals in the same event at the Winter Olympics.
And Saturday’s three medals – after Izzy Atkin’s ski slopestyle bronze – made it the most successful day at a Winter Games for Britain. Super Saturday on ice and snow.
Britain now have four medals – three of them in skeleton, after Dom Parsons’s bronze on Friday – to equal the record haul from Chamonix 1924 and Sochi 2014.
And there is still over a week remaining and plenty of further opportunities.
Yarnold forecast the result earlier this week.
She added: “I dreamt a couple of nights ago that we were both on the podium together, but I was too worried to tell her that I’d foreseen it.
“We were both on there. I think I was first.
“I’m just overwhelmed. I’m so happy. We will be on each other’s mantelpieces forever more.”
For Deas it is also the realisation of a dream. The 29-year-old was tearful when she recalled a message she received from Yarnold when her friend and team-mate won in Sochi. Deas said: “She sent me a message saying that she wished I could have been there with her.
“It’s been a long four years but I knew that I could do that and I just had to keep believing.
“I can still remember exactly what it said. I’m just so glad that I could be here this time around.”
Yarnold was 0.10 seconds behind Loelling overnight, despite complaining of being dizzy, but the German erred on the third run and Flock took a 0.02secs lead over Yarnold.
A scintillating fourth and final run from Yarnold, who clocked a track record of 51.46, saw her lead by a huge margin of 0.45, piling the pressure on Flock.
And Flock floundered as Deas endured the emotional rollercoaster of despair followed by jubilation among the sizeable British contingent present.
“I didn’t think I’d done enough,” said Deas.
“I knew my only chance was that Janine was going to make a mistake.
“I didn’t really want to believe it was actually going to happen until she crossed the line and I saw that she dropped behind me and I just couldn’t believe it. I thought ‘this must be a mistake’.
“I can’t believe I am part of a Super Saturday, I never thought I’d be saying that.
“I’m just extremely proud to have played a part of an historic day.”
Yarnold is now Britain’s most decorated Winter Olympian, after her first win since returning from her year-long sabbatical in 2016.
Only figure skaters Jeannette Altwegg and famous pair Jayne Torvill and Christopher Dean, who have one gold medal and one bronze each, also have multiple medals for Britain.
Whether either Yarnold or Deas go on to Beijing 2022 is doubtful, but both are fully fledged members of a skeleton dynasty which means Britain have won medals at every Games in which skeleton has been on the programme, dating back to the 2002 Winter Games in Salt Lake City.