Cannon was first hospitalised in January after "mild" kidney failure and then returned for treatment for blood clots in February.
In March, Cannon revealed that doctors believe he has a "lupus-type" autoimmune disease.
Carey has now told Shape magazine how worried she was about Cannon during his period of ill health.
"It was really frightening," she said. "But he's feeling much stronger.
"He's taking better care of himself, eating a diet low in sodium and sugar, and getting more sleep."
Cannon previously revealed that doctors had ordered him to go on a new diet, and said: "No Happy Meals - I'm sad."
Watch a video of Nick Cannon being interviewed at the Nickelodeon Kids' Choice Awards 2012 below: