RENE RUSSO is riding high starring in the blockbuster new “Thor” movie – but not long ago the redheaded beauty was mired in the throes of a secret breakdown so severe that she became a virtual recluse, often refusing to leave her home or even get dressed, said a source.

The actress, 59, suddenly dropped out of show business in 2005, was seldom seen at Hollywood events and didn’t return until she played Thor’s mother Frigga in the 2011 super-hero hit.

“After a string of box office failures, Rene came home one day, curled up into a ball and didn’t come out of the house for months at a time,” revealed an insider. “It was more than facing a mid-life crisis – she was a complete wreck!

“She stopped functioning and went off the Hollywood grid. Close friends and family would find her curled up in a fetal position in the corner of her bedroom, crying.”

The actress – best known for her steamy clinches with Pierce Brosnan in the 1999 version of “The Thomas Crown Affair” – would call up pals in the middle of the night in tears, telling them how lonely she was.

“She would wear her bed clothes throughout the day – refusing to get dressed,” said the source. “It was a dire situation.”

Russo – now in comeback mode with her smash “Thor” sequel “The Dark World” and two more upcoming star turns – recently said that she left movies because she was “burned out” and wanted to spend time with her daughter Rose, now 20, and husband, screenwriter/ director Dan Gilroy.

But an insider confided that Rene was breaking down emotionally and physically.

“It took years, but her family, close friends and a therapist finally brought her out of her nightmare.

“Now she’s working out daily and leaves the house every day with the renewed confidence of an A-list actress.”