Nimoy, who famously played Spock, had chronic obstructive pulmonary disease, an illness his wife, Susan Bay, characterized as "terrible" in an interview with Inside Edition.
"You cannot catch your breath," Bay said, adding that Nimoy could barely do anything by the end. "He couldn't go out. For him to go from the parking lot to the movie theater, forget it."
Nimoy went public with the condition after being spotted in a wheelchair at the airport. It was the result of years of smoking, which he gave up three decades before his death.
"He was on a campaign to use his profile and make people think twice about lighting up," said Bay.
Bay said her husband was ready to die by the end.
"Did he say to you, 'It's time'?" asked Inside Edition's Jim Moret.
"Yes," Bay replied.
"Simple as that," Moret said.
"He didn't want to be confined to a wheelchair and not able to breathe," Bay said.
So Nimoy, Bay said, turned to his nurses for help.
"They keep adding a little more morphine over the period," she said. "He was in such a compromised situation that it did not take long."
She added: "I believe in dying with dignity. Leonard believed ... in dying with dignity."
Bay now appears in a public service announcement to warn about the dangers of smoking. She hopes by speaking out against it, more people will follow the words Spock made so famous — "Live long and prosper."