Demi Lovato, who has been outspoken about the toll bullying has taken on her in the past, may have been experiencing a resurgence of it on Twitter.

The troubled star, who announced the cancellation of her tour last night and entered a treatment facility for "emotional and physical issues," quit Twitter just days before.

Could bullying on Twitter be one of the reasons for her breakdown?

Lovato, who said she was a victim of bullying, recently wrote an open letter as part of the Pacer Center's campaign, Teens Against Bullying:

    “People say sticks and stones may break your bones but names can never hurt you, but that’s not true. Words can hurt. They hurt me. Things were said to me that I still haven’t forgotten.”

Just one day after rumors that Lovato was hooking up with Justin Bieber hit the web, Demi deleted her Twitter.

From the road, Demi even tweeted that she was "missing someone back home," perhaps a reference to Bieber, whom she apparently gushed to friends was "a great kisser" and "mature for his age", reported Life and Style.

As we all know, rabid Bieber fans have been known to threaten his crushes online (Kim Kardashian even received a "death threats" after Justin posted a picture of them together with the caption "my girlfriend".)

But Bieber fans may not be the only ones who were taunting Demi on Twitter.

It's bad enough that Demi had to travel the world on tour with her ex-boyfriend, Joe Jonas. But then he went and brought his current girlfriend, Ashley Greene, along with him. Demi had admitted to Teen Vogue in the past that it "sucked watching" her ex with other women... and it must have sucked even more to see it at such a close range, when you're thousands of miles away from home and your support system!

And on the first night that Demi canceled her scheduled appearance, Greene tweeted a picture of the Jo Bros from backstage, writing:


At this point, Ashley must have known what was going on with Demi. So was this intentional? Probably not. But definitely insensitive.

We contacted the Pacer National Center for Bullying Prevention for a comment, and they simply said, "Our thoughts are with Demi and her family and we wish them all the best."

But we can't help but wonder if attacks on Twitter helped pushed the already unstable Demi over the edge...