Joan Rivers -- Melissa Sues Clinic Over Mom's Death

Melissa Rivers has just filed a huge lawsuit against the clinic where Joan Rivers' heart stopped beating ... and Melissa's lawyer says the doctors acted like a bunch of groupies and not medical professionals.

The lawsuit -- obtained by TMZ -- claims gross medical malpractice, alleging during the 20 minutes doctors tried to bring Joan back to life, they didn't think to perform a tracheotomy, which facilitates breathing.

Melissa says, "The level of medical mismanagement, incompetency, disrespect and outrageous behavior is shocking and frankly, almost incomprehensible," adding, "Not only did my mother deserve better, every patient deserves better."

In addition to suing the clinic, Melissa has sued Joan's personal doctor, Gwen Korovin. According to the lawsuit, she should not have been permitted in the room where the procedure was being performed, yet she jumped in and announced, "I'll go first."

The suit claims another doctor took cellphone pics of Rivers before the emergency, while she was under sedation, with Korovin in the photos, saying Joan "will like to see these in the recovery area."

According to the lawsuit, Korovin left the room in the middle of the emergency and the allegation is that she left because she knew she wasn't supposed to be there in the first place and "wanted to avoid getting caught." The suit says Korovin simply abandoned Joan.

And get this. According to the suit, in the middle of the emergency, another doctor took issue with a colleague who wanted to scope the affected area, saying, "Renuka, you're such a curious cat. You always want to know what's going on." The suit says the doctor refused to authorize the scope.

Melissa's lawyer spoke to The NY Daily News, which broke the story, and quotes lawyer Jeffrey Bloom who says, "Had doctors acted as physicians for Joan Rivers instead of groupies, Joan Rivers would have been doing 'Fashion Police' last week."

Yorkville Endoscopy has been under intense scrutiny and they are set to lose their accreditation at the end of the month.