Sources tell us Williams is getting treated in a facility just outside of Los Angeles and has been there for the past several days. Michelle has been open with her struggles in the past ... revealing her battle with depression in an interview last year.

In a statement Tuesday, Michelle says, "For years I have dedicated myself to increasing awareness of mental health and empowering people to recognize when it's time to seek help, support and guidance from those that love and care for your wellbeing."

She continues, "Today I proudly, happily and healthily stand here as someone who will continue to always lead by example as I tirelessly advocate for the betterment of those in need."

Williams famously reunited with Beyonce and Kelly Rowland at Coachella in April ... the first time the group had performed together in several years.