A Pilates instructor who suffered from a rare disease leaped to her death Thursday from her Upper West Side apartment — nearly crushing a horrified passer-by on the street, cops said.

Juilliard graduate Samantha Cohn, 34, crawled out a window in her 16th-floor apartment at West 71st Street and Broadway and jumped at 10:10 a.m.

Cohn, who was wearing workout clothes, landed on the sidewalk on Broadway and nearly hit a neighbor, Matt ­Kovary.

Her mother told investigators she had been diagnosed with Cushing’s syndrome, police sources said.

Cushing’s syndrome is a disease caused by exposure to high levels of cortisol. A tumor grows in the pituitary gland and causes serious side effects.

“I thank God for sparing me because I would be dead, too,” said Kovary, 59, who was on his way to the Upper West Side Copy Center on Broadway. “I heard a loud explosion. It was right behind me.

“I turned to see what the explosion was. The sight was so horrific. She was just at my feet. She almost took me with her.”

Stunned, Kovary headed to church after the tragic incident and prayed for the pretty victim.

“I’m so shaken from it. I went to church twice and prayed to God to save her soul. I could have been dead, killed an hour ago,” he said.

Cohn had gone missing for a week in April, prompting her worried mother to search for her and alert authorities, said a worker at her building.

“They found her in the hospital, supposedly for heat exhaustion,” said a doorman, Jacques Tassy. “When she came back [home], she seemed different. She wasn’t smiling as much.”

A woman who had been checking on Cohn regularly showed up on Thursday — 30 minutes after she had jumped.

“It wasn’t Samantha Cohn, was it?” the woman wailed. When she found out it was, she burst into tears.

The beautiful brunette spent more than 10 years as a professional dancer before teaching Pilates at Back in the Game Therapy near Rockefeller Center, according to the center’s website.