Former Goodies star and nature presenter Bill Oddie has revealed he has been "very ill" during the summer with an "almost fatal" condition.
The 79-year-old birdwatcher and conservationist tweeted he had been suffering from "lithium toxicity".
He wrote: "Just so you know, I have been very ill most of this summer. Lithium toxicity. Almost fatal!"
Oddie has spoken previously about having bipolar disorder, for which lithium is a common treatment.
It may also be used for depression, which Oddie has also had.
"I am still here but very confused about most things! But then aren't many of us," he wrote.
"IT fuddles my brain. Confusion. Will I return? I Really dunno. I do hope so. Please wish me luck. XX."
What is lithium toxicity?
Lithium is a type of medicine known as a mood stabiliser. It is used to treat mood disorders including mania, depression and bipolar disorder.
The NHS warns that if you take too much lithium, you should call 999 or go straight to A&E, even if you do not feel any different.
This is because very high amounts of lithium can cause problems with your kidneys and other organs. It can cause symptoms such as:
Feeling or being sick Problems with your eyesight (blurred vision) Increased need to go to the toilet, incontinence Feeling faint, lightheaded or sleepy Confusion and blackouts Shaking or muscle weakness, muscle twitches, jerks or spasms affecting the face, tongue, eyes or neckSource: NHS
The TV presenter had last tweeted on 22 June.
Ten years ago, Oddie said he had endured "probably the worst 12 months of my life" due to his struggle with depression and bipolar disorder, having spent two periods in hospital in 2009.
Oddie found fame in the 1970s as a member of comic trio The Goodies, alongside Tim Brooke-Taylor, who died earlier this year, and Graeme Garden.
Later in his career, his love of birds led him to present several shows on the BBC, including Bill Oddie Goes Wild, Springwatch and Autumnwatch.
If you have been affected by any of the issues in the story, you can access support via the BBC's Actionline.