Zosia's been displaying some unusual behaviour for a while now. What made her father, Holby boss Guy Self (John Michie), consider that something might be seriously wrong?
"Guy's witnessed Zosia spiral out of control as she began taking drugs, almost put patients at risk and, recently, almost burned down her flat! Guy then watched a video diary Zosia had made, in which she described what's going on in her head, and he saw that his little girl needed help."
Guy sent Zosia to rehab and, as she prepares to leave the clinic this week, Zosia receives a shock diagnosis...
"We finally discover the truth behind why Zosia does the things she does when she's diagnosed with bipolar hypomania, which is a mental illness. Zosia's terrified of her ability to lose control, but she doesn't want to admit she's got this problem; that scares her more."
Guy reluctantly lets Zosia return to work at Holby. Does she fear her diagnosis will affect her ability to be a doctor?
"Absolutely! It's frightening for Zosia to be so knowledgeable about the brain, psychology and wanting to work in that field, while knowing that she herself is so mentally unstable. It leaves her wondering: 'How can I understand other people, if I can't understand myself?'"
Guy's reassured when Zosia convinces a patient to have an operation. But, once in theatre, Zosia becomes disruptive and Guy's forced to throw her out...
"Because of her illness, Zosia experiences waves of clarity where she feels almost super-human and everything makes sense. But then she starts talking at 100 miles an hour and can't work out why people don't understand her. Playing Zosia in this state has been exhausting!"
As part of her treatment, Zosia's psychiatrist prescribes talking therapy and a course of Lithium tablets. Why is Zosia so against taking the pills?
"Thousands of people die each year because they avoid taking Lithium, a mood-stabilizing drug, as they can't face becoming a shell of their former selves. But, following her outburst in theatre, Guy steps in and tells Zosia she needs to take these pills. He has to be cruel to be kind."
What does the future hold for Zosia?
"For Zosia and Guy, I hope this illness can in some way help them rebuild their strained relationship. I want Zosia to move in a positive direction - it's important for Holby to show that people with mental illness can be successful, can get help and that drugs aren't necessarily a bad thing."
Holby City continues on Tuesdays at 8pm on BBC1.
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