The 36-year-old revealed that it came about during a time she felt her life was "perfect".
"I don't know why my nervous breakdown happened at the end of the lockdown," she shared in a new interview with Extra. "I made it all the way through, everything was great and my life was perfect.
"I'm that girl that when everything is going great, I need to f*** it up a little and make everything a little bit worse in my life. I am an addict and had thought that I had enough time under my belt, and I could drink like a normal person. And it turns out, I cannot, and I will never be normal."
Watch: Kelly Osbourne says she's relapsed after nearly 4 years sober
Osbourne told fans last week that she wanted to stay truthful by opening up about her relapse.
She's now said that by holding herself accountable and "owning" her journey, she can help other people who may be struggling.
Going into further detail on what triggered the relapse, the star - who is dating skateboarder Erik Bragg - said: "I got all of my career goals happening… and then I got happy cause I got this incredible boyfriend and everything in my life is so great and I’m like I’m not an addict anymore… On top of that pandemic fever… It all just got too much.”
Her younger brother Jack has also battled addiction issues and marked 18 years of sobriety last week.
He wrote in an Instagram post: "It’s not that it get easier or harder, It’s just that it’s life on life’s terms. If anyone is trying to get sober, know that it possible if you are willing to do the work.
"Sending lots of love to my people who have been on this journey with me. #sobersbetter."
Watch: Sharon Osbourne plans tell-all book after The Talk exit