Clarkson, 60, said that four days before Christmas he'd woken up in the night to find his sheers were 'soggy', and also developed a 'constant dry cough'.
He was then tested for the virus, and the result came back positive.
Writing in his column for The Times: "The doctor was very clear... I'd feel under the weather for between five and 14 days and then I'd either get better or I'd have to go to hospital."
His main concerns stemmed from his age and his lifestyle choices such as smoking.
Also, Jeremy expressed his concerns he had suffered with pneumonia twice in his lifetime.
"Where, because I am 60 and fat, and because I've smoked half a million cigarettes and had double pneumonia, I'd probably die, on my own, in a lonely plastic tent."
Clarkson said he self-isolated, heading off to bed with a new book to 'wait for the Grim Reaper to pop his head round the door'.
"I'm not going to lie - it was quite scary," he said.
"With every illness I've had, there has always been a sense that medicine and time would eventually ride to the rescue.
"But with COVID-19 you have to lie there, on your own, knowing that medicine is not on its way and that time is your worst enemy."
While Clarkson initially didn't feel too bad, his breathing started to become 'laboured'.
He said the doctor's grim warning about how it might suddenly get worse kept ringing in his head.
Clarkson admitted that he didn't even know if he was better now, saying how he's learnt over the past few days that there's simply so much we don't know about the virus.
"We don't know how long the antibodies last," he added.
"We don't know how easy it is to catch it twice. And we certainly don't know if any of the vaccines will work long-term. I don't even know if I'm better now."
Clarkson has been self-isolating at a cottage with his girlfriend Lisa Hogan and her children.
Featured Image Credit: PA
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