Now retired, Thornton recorded his biggest career success at Cheltenham in 1998 aboard Cool Dawn for the late Robert Alner, beating Strong Promise by a length and three-quarters.
Speaking on a special 'Get Inside' programme broadcast on Attheraces.com on Friday, Thornton said: "Two weeks ago today I was starting to feel run down and tired and aching, and a couple of days later the tickly cough started.
"The fever - I was drenched from head to foot, so Yvonne (wife) was sleeping in one bedroom, I was in another, different bathrooms, eating in different places. Harry (son) was coming nowhere near me.
"I'm just starting to feel better now, all I can echo to people is you cannot be too careful, because it does knock you sideways.
"It was a case of getting out of bed and brushing your teeth and I was out of breath, difficult to breathe and it does just knock you sideways.
"Even now I'm still sleeping probably three hours during the day and another 10 hours at night, so it does take it out of you."
Thornton, 47 - now a successful presenter with Sky Sports Racing - added: "Something like this (coronavirus outbreak) is going to transform our lives for years to come, I feel, people are going to have to be an awful lot more careful until they find an antidote for whatever it is.
"That's the thing, it can affect anybody - it doesn't matter how old you are or how young you are.
"If you do happen to get it at home, try to distance yourself from the people who live in the house as much as possible. Don't get in contact with anyone else - we've got to stop this and everyone has to work together.
"That's the only way it's going to happen, if people listen to what the guidelines are."
