"It was a scary, scary feeling," he recalled. "I got very lucky that there was a doctor in Orange County that had a test and was able to do one. I got my results two days later."
"It was like I had access to only 20 percent of my lungs," Underwood said. "The reason why the coughing is so scary and so hard to deal with is because when you cough, you can't get that air back as quickly as you normally can."
"I think, for me, the scariest part is actually feeling yourself breathe. We take it for granted, but everyday we just breathe naturally and we don't think about breathing in and breathing out. I had to make sure every single breath counted," he added. "I sort of had to re-teach myself how to breathe differently. It was the strangest feeling."
Concern for his own health was just one aspect of the fear Underwood experienced following his diagnosis.
"I tried to put a brave face on just because Cass and her family [were around], and especially at that time, I didn't know if they were going to be getting it," he explained. "I was scared for them. I was scared for myself. I think the scariest part was the unknown."
"Nobody knows what this thing does, how long it's going to last, if it has any permanent damage," Underwood continued. "I mean, I don't know if I could get it again or if I could relapse. So, it's just a scary time right now and I think that's like the most frightening thing for everybody."
Underwood remembers seeing false reports in the media about how coronavirus didn't really affect the young people. While the older population and those who are immunocompromised are more at risk for the disease, young people can still contract it -- and pass it on to others. He decided to post about his diagnosis on Instagram to get the word out about the dangers of COVID-19.
"I wanted to let people know that's not the case, that there's a strain or mutation or whatever we wanna call this virus, that was attacking my lungs viciously," he explained. "I wanted to make sure that everybody was playing their part and staying inside or doing what they could to practice social distancing -- not only for the elderly and taking care of those people, but taking care of your health as well."
Underwood slept for 16 to 17 hours per day in the first days after this diagnosis, with the Randolph family "nursing me back to life," he said. So far, Randolph and her family haven't shown any coronavirus symptoms.
"It's been so incredible, literally having [Cassie's mom] Amy be my little nurse and Cassie be there for me. [They have] masks and gloves on, supporting me and eating breakfast with me six, seven feet apart. And [her dad] Matt has made some killer food for me while I was recovering," he shared. "It's been as fun as you can make it in quarantine and isolation. But they've kept me in really good spirits."
"I am doing so much better. Cassie's family, I have to thank for that because they literally nursed me back to health and I don't know what I would do if it wasn't for them, so I am doing so much better," he declared.
Through it all, Underwood has been gearing up for the release of his book, The First Time: Finding Myself and Looking for Love on Reality TV, available now.
"I'm excited, I'm anxious, I'm nervous," he said of the book's release. "It was kind of me taking back ownership of my story. It's also my way of closing a chapter of my life, and that's with the Bachelor franchise. But I hope people enjoy it. I've definitely left very little to the imagination after this book, so hopefully it could help one or two people and people find it interesting."
"There's a lot of little things in there that I feel like can help a lot of people," Underwood said, before thanking his friends, family and Bachelor Nation for making the book possible. "Whether you liked me or didn't like me in those three seasons [on Bachelor shows], thanks for being there with me and going on that ride with me. And thanks to the show. I have mixed reviews when it comes to [my time with the franchise], but at the end of the day, I'm very happy and very in love with Cassie and I have them to thank for that. So, I just wanna say a big thank you."
The First Time: Finding Myself and Looking for Love on Reality TV is now available where books are sold.