In agreement with another reviewer, I think that readers who appreciate Sylvia Plath (The Bell Jar) will also find Beyond the Glass worth reading.
Aside from the excellent writing skills they share in common, something intriguing about Plath and White is that they both have events leading up their so-called "madness" which seem to have been overlooked by their doctors. Although I would hope that times have changed...all too often, it seems that modern medicine is prepared to cry "insanity" before actually doing a thorough investigation of possible root causes.
Reading Beyond the Glass, I was - over and over - struck by White's descriptions of an ailment which seems thyroid-connected. She mentions severe listlessness, sudden weight gain, changes in her hair, skin, eyes, and nails, depression, constantly being cold as ice, and more. Anyone with a long history of autoimmune thyroid disorders (and obviously, there are plenty of us out here) will start to wonder, or at least, that's what I assumed. However, when I looked around on-line, hoping that something had been written about Antonia White's thyroid disease, all I could find were articles about her mental illness. And there is no question that, especially as the story deepens, Clara is mentally ill. (Antonia White wrote the book later in life, based on her own experiences as a younger woman - and calls her character "Clara.")
The question is why - *why* is she mentally ill. And I still think her thyroid - perhaps - has a lot to do with it. Conditions like Hashimoto's Thyroiditis can cause intense swings from hypothyroidism to hyperthyroidism - and when Clara shifts into a "manic" state, what kept screaming off the page (at least, from my perspective) was severe hyperthyroidism. I will certainly admit that it may be hyperthyroidism AND other things, but it still seems to be heavily in the mix. Suddenly she is losing tons of weight as if by magic, has so much energy that she seems to be on speed, is hot all the time (even to the touch), has serious insomnia, suffers breathlessness and heart palpitations, and can't keep her hands from trembling.
What happens in Clara's life after that is so extreme that, really, you will have to read the book. I can't put it into words, and White did such a beautiful job that there's no purpose in messing with it. And even with all that happens in Nazareth Royal Hospital (Bethlem Royal Hospital/Bedlam, in real life), as "crazy" as it sounds, I still stand by the suspicion that somewhere in the root causes of this supposedly bipolar madness, there's an endocrine disorder.
And as far as the connection with Plath, I am extremely curious about the connection of Sylvia's initial toxic exposure during a near-fatal shellfish poisoning with her ensuing "madness." Yes, she may have been high-strung and prone to the somewhat "normal" melancholic bent of a writer before that episode - but I have read her diaries and letters, and I don't think she was ever crazy. Her nervous system was seriously assaulted by some rotten shrimp, and she was never the same afterwards. No one who knew her thought so, either - at least from what I found.
I'd be interested to hear if other readers locked on to the same medical details, and what they made of them.
All this to say: whether you're interested in the medicine or not, read Plath and White. You'll find it well worth your time. They can write, and I'm certainly glad they did. If only the personal cost had not been so high for both of them.