Britney Spears' story is worth a lot of dough -- but she's forgoing a payday to sit down and speak her truth ... and instead, doing an impromptu YouTube dump that's 20 minutes long.

The singer posted a 22-minute clip on the video platform Sunday out of nowhere, and if you watch it -- you'll see she's spilling her guts about everything ... with specific focus on how exactly the conservatorship started and what she remembers during those many years.

BS starts out by saying that she's got a lot on her mind, and noting that while she's been offered lucrative deals for exclusive interviews -- like with Oprah, for example -- she says she finds that notion "irrelevant' and apparently thinks selling your story like that is tacky.

Instead, she's giving it straight to the people ... diving into how things started when she was spiraling in the mid-2000s. She says when the conservatorship began, she didn't understand why ... but all of a sudden, her dad was running the show and was very controlling. Britney claims he told her, "I'm Britney Spears and I'm calling the shots."

She also says a woman introduced the idea to Jamie, and that her mom helped him follow through. Britney calls it "pure abuse" and recounts being held down on a gurney as paparazzi and helicopters swarmed her pad the day she was put in a psychiatric hold.

Speaking of paps, Britney says this of her infamous episode ... "The extent of my madness was playing chase with paparazzi, which is still to this day one of the most fun things I ever did about being famous." She says she doesn't know what was so harmful about that.

She goes on to describe what it was like working under the conservatorship, and it sounds miserable. Britney says she felt like a robot who was under the direct control of her father.

Britney says that after her Vegas residency ended in 2017, a new show was in the works ... and she says that when she was rehearsing for it, she stood up for herself about a certain dance move -- saying she simply voiced her preference. After that, she says she was shipped away to a facility, under the guise of seeking treatment and worrying for her dad's health.

While there, Britney says she was heavily medicated ... this after she claims her father threatened her with a major legal battle that he thought she's apparently lose.

This was a particularly dark chapter for her, Britney says, and it's clear Britney resents her family for putting her through that -- especially her mom, whom she says turned a blind eye. Remember, photos from that specific period showed Britney appearing very out of sorts, when her then-boyfriend Sam Asghari took her out for a bit around Easter time.

Britney describes more conditions placed on her during the conservatorship ... including absolute control of what she ate, where she could be, her schedule, her company, everything.

It was around this time -- 2019/2020, when the #FreeBritney movement was in full swing -- that Britney says she finally felt confident enough to take control of her life and attempt to get out of the conservatorship. She even shouts out #FreeBritny protesters who backed her.

Britney says she believes Jamie and co. thought she'd come crawling back and get into the cycle she'd been in for years, but instead ... BS says she got a lawyer and held her ground, refusing to fall back into their clutches and actually try to retake the reins of her life.

It's a lengthy confessional, but Britney's getting into all of it here ... more than we can write to in this post. As we all know, Britney did break free from the conservatorship in the end -- and now, she's telling her story on her own terms. And we're sure it's far from over too.