The music mogul has cut down on cigarettes, goes to bed earlier and enjoys bike rides with his son, Eric.
The multi-millionaire also said he wants to “live for ever” – and credits the NHS with saving his life.
Cowell was forced to miss The X Factor live shows after the collapse in October last year. He has said his fainting spell was caused by low blood pressure.
The judge on the reality television music competition had woken up feeling poorly and gone downstairs at his west London home to get hot milk.
He felt dizzy as he walked back up to bed and the next thing he knew, paramedics were putting a neck brace on him.
It was initially feared he might have broken his neck.
Cowell, 58, said: “It has changed me. The crazy late nights working, [now] no more late nights – and I’m getting up earlier.
“I feel a million times better, genuinely. You reach a point and you go, ‘What’s all this for?’ You don’t want to kill yourself working.”
Simon was speaking at the unveiling of new X Factor judges, Robbie Williams and wife Ayda Field and former One Direction star Louis Tomlinson.
“I always had a good time but this was a wake-up call.”
He says of the NHS, which is celebrating its 70th birthday this year.
“It saved my life I came out feeling better than when I went in.”
Cowell now says he is also inspired by his four-year-old son with partner Lauren Silverman.
“I want to see life through Eric’s eyes,” says Simon.
“I am going to live forever now.
“I want it to be uncomplicated, I want it to be fun because he is fun.
“He is happy and, without question, the best thing I have in my life.
“I adore him. We go cycling to the park and I’m doing exercise.”
The boss of the Syco entertainment company is now back on form and has high hopes for the next series of The X Factor.
“This is the best panel we’ve had in a long time. It’s back to the old days,” he said.