"She said [Christopher] Reeve, making one of his first screen appearances, became irritated whenever she would read during breaks."

"He’d say, ‘You don’t stay in character?’ I’d say, ‘For Christ’s sake, Chris, I’ve been Lois Lane for a year, all you do is look left, I can handle it.’ And I’d pull out my book and he’d get very cross."

From "Margot Kidder, who played Lois Lane in blockbuster ‘Superman,’ dies at 69" (WaPo).

Also:

[I]n 1996, she endured what she later jokingly called the “biggest nervous breakdown in history, bar possibly Vivien Leigh’s,” a reference to the troubled “Gone With the Wind” star. “If you’re gonna fall apart,” she advised, “do it in your own bedroom.”

Her collapse, she said, was triggered by a virus on her laptop that erased years of work on a memoir. The loss sent her spiraling. She became convinced that her first husband, author Thomas McGuane, was trying to kill her with the help of the CIA. She slashed her hair and removed several teeth in a bid to go unrecognized.

Over the course of three days, she wandered the streets and narrowly escaped being raped. She was found disheveled, penniless and disoriented in the back yard of a home in Glendale, Calif., and was taken to a private psychiatric clinic for evaluation....

That's the detail I never forgot about her: She was so mentally troubled that she pulled out some of her teeth. I looked to see if pulling one's own teeth is at all common in mental illness. What I found was "Pulling Teeth to Treat Mental Illness" (The Atlantic):

As medical director of the New Jersey State Lunatic Asylum in Trenton between 1907 and 1930, [Henry Cotton] routinely practiced what he called "surgical bacteriology," the extracting of potentially diseased parts of the head and body, based on the observation that people who run high fevers sometimes suffer hallucinations.

This "focal infection therapy" seemed so scientific and promising that Cotton and his assistants yanked more than 11,000 teeth.... Cotton's experiments were unethical and awful, but they weren't that illogical if you consider the knowledge that was available at the time....

If you had no idea about neurotransmitters or lobes, it makes a weird sort of sense that micro-infections in the head would be the true cause of schizophrenia... [W]e still don't know, say, the very best way to prevent schizophrenia....

But it doesn't say that Kidder had the deranged idea that her teeth were the cause of her psychological distress. It says she was trying to change her appearance so people wouldn't recognize her. I question the accuracy of that report (especially since it had to come from the person who was mentally ill enough to subject herself to such a painful, damaging ordeal).