The 43-year-old, whose full name is Melanie Brown and performed as Scary Spice, told The Sun on Sunday that she's been through an "incredibly difficult" six months in which she worked on an autobiography.
"It has been unbelievably traumatic reliving an emotionally abusive relationship and confronting so many massive issues in my life," she said.
Brown posted a link to a US government website to Twitter explaining post-traumatic stress disorder (PTSD) after she was diagnosed with it following an abusive relationship.
"Knowledge is power," the singer wrote.
She was married to film producer Stephan Belafonte from 2007 to 2017, having split in 2016. The couple featured in a reality TV show on E! channel in 2010 called Mel B: It's a Scary World.
Brown said the course of rehab treatment was "really helping" her, adding she's "fully aware" she's at "crisis point" and had been using alcohol to "numb my pain".
The singer took out a temporary restraining order against Belafonte in April last year, whom she claimed subjected her to years of physical and emotional abuse.
According to the LA Times, Brown said Belafonte choked and punched her, forced her to lie about injuries, impregnated their nanny, hounded her to engage in threesomes with other women and secretly recorded sex tapes which he threatened to release to destroy her career.
A domestic violence trial was settled out of court last year, the Guardian reports. Brown said the ordeal was emotionally draining and claims she was "financially battered" by it.
She says she hopes to become "a better version of myself for my kids, for my family and for all the people who have supported me in my life", reflecting on her reasons for entering rehab.
Last year an Australian stripper spoke to media about an alleged threesome she had with Brown and Belafonte.
In another claim, English socialite Lady Victoria Hervey told media she had a threesome with the married couple in 2007, adding that she felt "terribly" for Brown, who wasn't "strong enough" to leave Belafonte.
Brown has had a successful solo career outside of the Spice Girls group, most recently co-presenting America's Got Talent and appearing in a Broadway production of Chicago.
There are rumours of a Spice Girls reunion in the UK.