Lyme disease is a bacterial infection that can spread to humans via a tick bite.
The disease can be easily treated if detected and diagnosed early, but for a long time, the actor did not know what was causing her to feel unwell.
It often starts with a circular rash and can cause flu-like symptoms, nerve pain and sometimes a droop (facial palsy) on one, or both, sides of the face.
Symptoms are often short-term and can be alleviated by antibiotics, but some go on to suffer long-term symptoms, including chronic tiredness and unexplained neurological issues.
Speaking about her marriage, she said: “The reason I put this little love story of mine in it was mainly because at the beginning of the book, yeah, I’m alone. I’m bed bound by this illness.
“And waiting in the darkness in a confusing place gives you the chance to long for what you want to do. And I realised I didn’t want to be alone.”
She added: “I really recommend it, honestly, getting married in the midlife is a full injection of joy and fun. It’s the best.”
The actress, who began her career performing at the Edinburgh Fringe in the early 2000s, portrayed the unlucky-in-love and socially awkward Miranda in her TV sitcom, which ran from 2009 to 2015.
I Haven’t Been Entirely Honest With You is published on Oct 10.