Demi Moore was held down by terrified friends while her body was wracked by convulsions that left her unable to speak — a frantic phone call to emergency services reveals.
The bombshell ten-minute audio recording of the call suggests the star had smoked an unspecified substance before collapsing.
But a US website claimed she inhaled nitrous oxide — also known as laughing gas — which is popular with youngsters in search of a cheap high.
Demi has also reportedly been taking prescription drug Adderall, an amphetamine-based medication for treating attention deficit hyperactivity disorder and narcolepsy.
Paramedics were called to the Ghost actress's Los Angeles home at 10:45pm on Monday night.
Five people are heard on the tape obtained by website TMZ. Three of them are with the stricken star, the other two are emergency operators.
Friends are heard in the call speaking to someone called Ru in the house, suggesting her daughter Rumer Willis, 23, was present.
The recording begins with protracted discussions about the 49-year-old's exact address before the first voice heard says: "She smoked something. It's not marijuana.
"It's similar to incense and she seems to be having convulsions of some sort."
The woman then tells the operator that the actress is "semi-conscious".
When asked whether she was breathing, the operator is told: "She's convulsing."
She repeats that Demi "smoked something" before going on to say that her reaction is "accidental".
The phone is passed to another woman who informs the operator Demi is "burning up".
When asked by the operator if Demi can respond to her, she says: "Yes, she's squeezing my hand, but she's not able to speak."
She next tells the operator that they have pinned the actress down due to her convulsions but the operator tells them not to.
The phone is then passed to another person who reveals the star's condition is improving.
He said: "She seems to have calmed down and she is speaking.
"Now she's breathing fine. She's not convulsing and she's talking well."
Demi split from her husband Ashton Kutcher in November.
He was accused of cheating on her with Sara Leal, 23, on their sixth wedding anniversary in September.
Since she was admitted to hospital Demi's spokesperson issued a statement saying she was now seeking help to treat "exhaustion".
She said: "Because of the stresses in her life right now, Demi has chosen to seek professional assistance to treat her exhaustion and improve her overall health."
Kutcher, 33, was partying in Brazil when she was rushed to hospital. He arrived back in LA on Thursday amid suggestions he planned to visit.
