"A lot of victims and survivors will say they detach and you really do," McGowan, 44, said Tuesday on "Good Morning America." "You float up above your body because you’re trying to figure out ... Literally when he grabbed me I was thinking, ‘Oh I hope I still have lipstick on for the camera.’"
"Your brain is in another place and all of a sudden your body is like, ‘What, what, what,'" she said. "This is not what I expected at 10 in the morning."
In a statement to ABC News, Ben Brafman, an attorney for Weinstein said, "Mr. Weinstein denies Rose McGowan’s allegations of nonconsensual sexual contact and it is erroneous and irresponsible to conflate claims of inappropriate behavior and consensual sexual contact later regretted, with an untrue claim of rape."
"We know that there is a neurobiological response when someone is experiencing trauma," said Laura Palumbo, spokeswoman for the National Sexual Violence Resource Center. "For many survivors they describe that as -- they couldn’t move their body or they were frozen or being unable to respond the way their mind was interested in because their body was immobilized.
"We also know that for many survivors, in addition to the feeling of being frozen, there is an experience of detachment, trying to detach from the trauma and violation that the body is experiencing," Palumbo added. "Some would describe it as an out-of-body experience, some describe it as their mind is in another room."
Response depends on 'reflexes and habits'
Researchers in Sweden tracked nearly 300 women who visited an emergency clinic for rape victims. Of those women, 70 percent reported significant tonic immobility -- which the study authors defined as "involuntary, temporary motor inhibition" -- and 48 percent reported extreme tonic immobility during the assault, according to a study published last year.
Dr. Jim Hopper, an expert on psychological trauma who writes the blog "Sexual Assault and the Brain," studies the science behind the brain's response to sexual assault. His research has led him to train police officers, prosecutors and judges to better understand how victims of sexual assault may disassociate from the trauma, leading to a lack of resistance and gaps in memory and recall.
"There is a disconnection of awareness from what it would usually be connected to, so people can literally not feel the sensations or the emotions in their body," Hopper told ABC News of the experience of sexual assault. "So there can be pain, horror and fear and the next moment they feel nothing."
There is an evolutionary origin to these responses, dating back to co-evolving predators and prey and "survival reflexes" that can kick in, according to Hopper, who is a teaching associate at Harvard Medical School.
"One extreme survival reflex is dissociation, in which, as Rose McGowan described, awareness disconnects from painful and horrible sensations in the body," he said.
"When a predator has its prey in its jaws -- or a perpetrator is holding you down and raping you -- that can trigger really extreme survival reflexes," he said. "The prey stops moving in ways that can help not trigger further attack and killing by a predatory animal."
People who commit sexual assault, though, often don't care if their "prey" is not responding, Hopper explained.
"With a sexual predator, these things that evolution put into our brain to stop predators that want to eat us render us incredibly vulnerable to someone who doesn’t care about our pain or how we’re responding," he said. "They don’t care if you’re a body that's paralyzed or gone limp or you’ve checked out. He’s still getting his conquest and may even get off on your inability to resist."
Dissociating is a common response of many sexual assault victims but not all, experts say.
"The bottom line is you cannot predict how any one person is going to react," said Dr. Gene Beresin, executive director of Massachusetts General Hospital's Clay Center for Young Healthy Minds.
Beresin's research has found that a person's reaction to such assault is affected by both internal factors, such as their personality and any prior experience of trauma, and external factors, like the individual's culture, community and concern about consequences for them.
The power of the perpetrator
Last month, 156 victims addressed a Michigan court saying former Olympic doctor Larry Nassar sexually assaulted them under the guise of performing medical treatments. Some of the allegations date back to the 1990s and many of the women who spoke claim the alleged abuse occurred multiple times.
Like Weinstein, a once-powerful movie producer, Nassar's power in the gymnastics world illustrates another factor that can affect a person's response during an assault -- the relative power of the perpetrator over the victim's life or career.
"They were powerful figures who were perceived by these girls and women as having a lot of power in a very high-stakes environment they’ve spent their lives reaching for," Beresin said of Weinstein and Nassar. "And that can result in paralysis and confusion."
The level of trust a victim seemingly has with the perpetrator may also spark a detached response, experts say.
"In addition to their trauma experience, this may be someone who they trust so it may be very hard for them to rationalize what is happening to them and difficult to deal with the reality," Palumbo said. "So they may just bring their focus and attention to something entirely outside of the scope of what’s happening as a way to preserve themselves from the trauma they’re experiencing, to draw their attention elsewhere."
Guilt over detaching
Some victims of sexual assault feel guilt or shame afterward if they froze or detached during the assault. They may wonder -- and be asked by others -- why they did not fight back, call for help or run away, experts say.
One reason that they may judge themselves in retrospect, Hopper said, is that the rational circuitry in their brain, the prefrontal cortex, was not working normally during the attack but returns to its usual functioning afterward.
"This is a brain under attack," said Hopper. "There's also a circuitry that allows us to know what’s going in our body, and there is some evidence that when people are in these states, there is less activity in that circuitry."
The brain's first response to attack, including sexual assault, is usually to freeze, which is a "stop everything" response that puts the brain into a mode of automatically looking for danger and escape options, according to Hopper. Then, what Hopper calls "stress chemicals" are quickly released into the prefrontal cortex, the part of the brain that handles rational thought.
That rush of chemicals impairs the prefrontal cortex, and can take away a victim's ability to think rationally about ways to escape the assault. In response, the victim may dissociate and become immobile, even literally paralyzed with fear, Hopper said.
Dissociation during an assault can affect a victim's attempts to recover.
"For some individuals, in the immediate experience they are bringing themselves outside of the moment but in the short and long term they can recall what they experienced and memories are very fresh," said Palumbo. "For other individuals with the response of dissociating, their ability to recall directly what they were experiencing might not be as straightforward."
She added, "Or it may be days, weeks or years after the experience that something else in their environment triggers very detailed memories of what happened."
What is most important to remember, according to experts, is that there is no single universal response to sexual assault."We should not assume that everybody is going to react the same," said Beresin. "We should assume that it is a horrible, shameful, destructive event that has an impact physically, emotionally, psychologically, socially and on one's identity."