From speeches watched by millions to a position as her party’s deputy leader at Westminster, Mhairi Black appeared to be one of politics rising stars.

However, away from the House of Commons the SNP MP was “flailing through life” and became ill through depression and anxiety, she has told the BBC.

Black believes it was only through a “life-changing” diagnosis of attention deficit hyperactivity disorder (ADHD) that she was able to regain control of her life.

The former Paisley and Renfrewshire South representative also said her party’s performance at last year’s general election, where the party dropped from 48 MPs to eight, was due to “self-inflected” woes.

Black stood down as an elected politician in 2024 after nine years, having first won her seat aged just 20.

She said her decision came after years in a “toxic” and “bullying” environment that was “consuming my entire life”, with her mental health suffering badly until she was diagnosed with ADHD around 2018.

“Everything was fried – my body, my mind was emotionally fried,” she told the BBC’s Scotcast podcast.

The interview comes ahead of the release of a new BBC documentary, Mhairi Black: Being Me Again.

She said: “I couldn’t go out without throwing up. I would have panic attacks everywhere I went.

“I didn’t understand what was going on and why I was feeling like this, I’m just beating myself up more, because I’m thinking, well, everybody else is managing to get into work okay. Why are you the one that can’t cope with it?”

The documentary – which will air on BBC Scotland at 21:00 on Sunday and is available on iPlayer from Friday – shows her discussing the condition and her last year at Westminster.

She describes how anxiety became depression, and saw her take time off from Westminster duties – a decision that brought criticism for her attendance record at parliament and holding a lack of surgeries in her constituency.

“Westminster didn’t have a capacity for signing off, so it looked to the rest of the world like I’ve no been turning up, when in actual fact I was in the foetal position in my house,” she says.

For Black, the diagnosis of ADHD has had a “life-changing” impact on her life.

She told Scotcast: “It was massive because it felt as though someone had just handed me the instruction manual for my own brain, and suddenly I was able to think like, I’m not mad, I’m just wired differently.

“It allowed me to stop beating myself up so much because there were times when I would struggle to do things that other folk do effortlessly.”

Black compares the condition to the BBC’s Sherlock series, where Benedict Cumberbatch’s famous detective would use his “mind palace” to work out cases.

“It feels like there’s constantly three conversations in my head – and a song,” she laughs.

However, Black told Scotcast she decided not to go public with her diagnosis at the time as it “would get used against me” in Westminster – an aggressive culture that her wife Katie was surprised by.

She recalls: “When she [Mhairi] started telling me about her experiences since being in parliament, I almost couldn’t believe what I was hearing.

“It was very different to what I’d believed. I was surprised how isolated she was.”

Black recounts seeing punch-ups and bullying during her time as an MP, and although she raised concerns with her party, the support offered was not enough.

She said: “I think leadership at all levels have been aware of people who’ve been unhappy with how they’ve been treated, and I imagine most people would agree that we could be better at how we handle it.”

Elected as the SNP dominated the Scottish vote, her departure from Westminster came on a night when, in her own words, “the SNP got an absolute doing”.

Black felt the SNP’s poor result happened due to “in-fighting that was spilling out into the public domain”.

She added that this was not helped by power being centred around leader Nicola Sturgeon and her husband Peter Murrell who was the party’s chief executive.

She said: “The reason that I think it spilled out into the public was because a lot of people had hit their limit because they felt like their voices weren’t being listened to within the party.

“There were a lot of folk who weren’t comfortable with the idea of the chief executive and the leader of the party basically being a couple in one house.”

Black added she believed the SNP worked best when on the left politically, and that if the views of current deputy Kate Forbes became party policy there would be a “mass exodus” of members.

Forbes is known for her conservative views on issues such as gay marriage, abortion and trans rights.

Black was a headline act from her first days in Parliament, when her initial Commons speech saw her decry poverty and was viewed 10 million times within days.

It came after a whirlwind time when she overturned Douglas Alexander’s majority in 2015, as part of an SNP surge that saw the party take nearly every constituency in Scotland.

Black had been energised by the independence referendum in 2014, which she calls a “magical” time.

Defeat in the independence vote “felt like a death” she says, but within months she was standing for election – a time that saw social media posts she made as a teenager resurface, including declarations of love for Smirnoff Ice and views on football.

“The way it was twisted to make her out be a drunken, bigoted wee lout was one of the worst times of my life,” recalls her father.

It did not hurt her at the polls though, and she carried that bluntness into her Westminster career.

However, a vulnerability was underneath the surface – at one point the documentary shows a stuffed panda bear given to her by her mum to keep her company in London.

In 2018 she spoke at length about the abuse she had suffered online, repeating some of the many foul-mouthed slurs sent to her about her appearance and sexuality, including that you “can’t put lipstick on a pig” and that she was “too ugly to be raped”.

“It’s difficult to describe how you can feel so alone and unsafe and under attack with nothing more than your phone sitting there,” she reflects.

“I get death threats all the time but there was one in particular where the police came to my flat down in London and the house up in Scotland.

“It was like two in the morning and the phrase used was a ‘an imminent death threat’.

“I don’t know what I’ve done to make you viscerally hate me that much.”

Since politics she has performed a one-woman show at the Edinburgh festival and spent time talking about politics on various TV shows and podcasts.

There does not appear to be any second guessing about her decision to stand down though, as she enjoys a walk with her dog in the new documentary.

“People deserve a representative that wants to be there and I don’t think that’s me anymore. I’ve done my bit,” she says.

“Doing something normal on a Tuesday, going for a walk with my wee best pal, is much better than running around Westminster.”

• From Friday, 7 March, watch former SNP MP Mhairi Black talk politics, neurodiversity and stand-up comedy in this very personal film on the BBC iPlayer.