He says he does not have "that much longer" in his first interview since revealing he has Parkinson's disease.
The Black Sabbath frontman also said his health is at the forefront of his mind, but does not dwell on his diagnosis.
Speaking to Kerrang Magazine, the 71-year-old said: "Do I ever think about when my time's gonna come?
"I think about it - I don't worry about it. I won't be here in another 15 years or whatever, not that much longer, but I don't dwell on it. It's gonna happen to us all."
He added: "Am I happy now? No. I haven't got my health.
"That thing knocked the s*** out of me, man, but I'm still here. In fact, I worried about [death] more when I was younger than I do now. I just try to enjoy things as much as possible, even though that's so f****** hard sometimes."
Osbourne also said that his daughter Kelly encouraged him to make music, adding that without that motivation, he may not be here today.
"I wouldn't be sitting here now if I hadn't made [music]," he said.
"If you saw me at the beginning of last year you'd think I was f****d. But I honestly think making this album is the best medicine I could have had. I was doing something, something I like to do.
"I wish I could do more, but it just felt great."
He previously revealed his Parkinson's diagnosis on Good Morning America, where he said he was forced to postpone his upcoming tour after being in hospital with pneumonia, but while recovering at home he fell over, which he said "screwed" all his nerves.
Osbourne also said that he is going to Switzerland to seek specialist treatment.
He made his first public appearance since the interview last week in Los Angeles where, joined by his wife, Sharon, he presented an award at the Grammy's.