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"There was a moment where I woke up at about three or four in the morning with the bed soaking wet from night sweats, and the symptoms of not being able to catch my breath hit me," Underwood, 28, detailed.
"I panic-bought oxygen on Amazon at four in the morning because I just didn't know how I was going to breathe," he continued.
When asked if his struggle to breathe was due to decreased lung capacity or anxiety, Underwood said he thinks "it was a mix of both."
"It was a little bit of a panic, but then the reason why the cough was so bad and so scary was because while you cough, you can't breathe," he explained. "…I see why people with pre-existing conditions can struggle from something like this because I felt like I was a healthy 28-year-old and it knocked me on my butt very quickly."
Underwood then offered a message to those that think their young age and fitness stand as a defense against the virus.
"… This is serious, you guys need to listen to your doctors and your medical professionals and stay inside."
Colton Underwood (ABC/Image Group LA)
As for where he contracted the virus, Underwood has no idea.
"That's the scariest part of it all," he said. "I don't know how, I don't know when, I don't know where it came from, how long I had it and how long it was sitting in me or I was infecting other people."
Underwood also revealed that his girlfriend, Cassie Randolph, and those that he's been staying with have all seemed to avoid contracting the virus, which he attributes to strictly following guidelines set by professionals regarding caring for someone infected by the coronavirus.