Nick Cannon says he could die if he doesn't pump the brakes on his career ... and the first step is quitting his gig on a NY morning radio show.

Cannon tweeted this morning, "The Doctors found blood clots in my lungs and said if I don't slow down and stop working so hard then it's a wrap!" Doctors also discovered an enlarged ventricle in Nick's heart.

Due to the diagnosis, the 31-year-old announced he'll be leaving his job as host of the "Rolling with Nick Cannon" show on 92.3 in NYC.

Cannon -- who will continue his gig with 'America's Got Talent' -- released a statement saying, "Under doctor's orders, I have been asked to cut back on some of my professional commitments to allow my body to get the rest it needs to keep up with the demands of my multitasking schedule."

He added, "Even Superman has to sleep."

It's not the first time Cannon has dealt with a medical scare -- he was hospitalized last month for kidney failure.