Los Angeles - Nick Cannon was hospitalised with blood clots in his lungs last week.
The America's Got Talent host - who suffered mild kidney failure earlier this year - was treated by doctors for two clots and an enlarged right ventricle in his heart after his immune system began attacking his organs.
Speaking on his 92.3 NOW-FM show, Nick - who has nine-month-old twins Mroccan and Monroe with wife Mariah Carey - said: "I have been in the hospital since Friday, and actually, it's quite serious. I didn't even know.
"I was actually trying to downplay it a lot - even in my own mind - not go to the hospital because I was having a lot of pain in my back and I thought it was the typical kidney pain that I had been experiencing, but I thought it had been a little bit heightened....
"Because of the blood clots in my lungs, I also had an enlarged ventricle in my heart
"My antibodies [in] my immune system were attacking my organs and it made my body even weaker."
'Work is going to kill me'
Despite his latest health scare, the 31-year-old presenter feels "lucky" because it could have been much worse.
He added: "My doctor was like, 'Luckily, you're in shape, because most people who get blood clots in their lungs can't breathe and they stop breathing, like, forever.'"
"I didn't have that symptom of not being able to breathe. I mean it hurt; I had pain; when I took deep breaths it really hurt, and I told my doctors about this and they hooked me up and everything's good now."
Nick has now been warned he has to slow down his work rate - or it will "kill" him.
He added: "My doctor was saying that my work is going to kill me - and he's not joking.
"I think part of the reason why my health did kind of deteriorate was because I wasn't resting a lot and I was doing too much. I was overworking myself, working out too much.
"I always took a lot of pride in working so hard and never taking a day off. But I'm learning that it isn't the wisest thing all the time, especially being a new father. Not only wanting to spend more time with my children, but wanting to be there for my children."