Despite developing a cough and breathing difficulties, federal regulations which deny access to those who have not traveled overseas meant his condition was not at first treated as a potential coronavirus case.
Watt, who referred to himself as a "fit, healthy young man" was eventually tested by a private doctor, resulting in a positive reading for the virus.
He told his 311,000 followers he's now using an oxygen machine to "give his lungs as much relief as possible".
"Yesterday I was given the results that I am positive for COVID-19. I wanted to tell you all about my journey getting here in an effort to bring awareness to the severity of what's happening in the world," he wrote.
Watt was told he had the flu and assured there was no way he could have COVID-19 because he hadn't left the country.
He clarified that he only visits his studio before heading straight home day by day.
Watt says he was prescribed over the counter cold and flu medications to fight the fever, but "the chills, sweats, and fevers," did not subside.
"I started to become delusional and then began the dry cough," he added.
Watt said he was rushed to hospital, where he "begged" for a COVID-19 test, but was turned down.
"I begged and pleaded to be evaluated and finally was given a chest x-ray," he said.
"The results of which were Viral Pneumonia … but still … No Test."
A private doctor tested him on Monday, and sure enough, the results were positive.
"I am laid out in bed chugging Gatorade and using an oxygen machine to give my lungs as much relief as possible," he wrote, before issuing a stern warning to anyone not practising social distancing.
"I am 29 years old. I am a healthy young man and I am going to get through this no matter what. I am going to make a full recovery," he wrote.
"But … there are so many people in my life and in the world that could possibly not get through this due to their age and/or a compromised immune system … this is why I am writing this post. I can't stress this enough … This is not a joke. Stay inside, stay sanitised."
Watt implored followers to take care of themselves and the people around them
"To have the mentality 'I'm young this can't affect me' is just straight up stupid and so dangerous to everyone around you," he said.
"Social distancing is to protect someone's mom and dad, someone's grandmother … it's not about you. It's about everyone together fighting this as a team."
Watt's post has prompted an outpouring of support from musicians including Katy Perry, who commented: "You got this Andrew! Love you and gonna pray for you," Perry said.
Blink-182 left a black heart emoji on the post, while Cardi B sent her well-wishes: "Hope you get better. Yes! You are so vibrant and full of life I know you can do it ! (sic)"
Model Gigi Hadid also offered her support: "Sending u strength & love Andy, hope u feel better soon brother (sic)."
