WWE's Nikki Bella Says Brain Cyst Is 'Super Scary,' But It's Benign

Nikki Bella says she's incredibly grateful the cyst doctors found on her brain is benign -- but going through the process was "super scary."

The WWE superstar first revealed her medical issue this week on "The Tonight Show with Jimmy Fallon" -- but she didn't really open up about the situation ... until now.

"They found a cyst on my brain, which thank god, it's benign," Nikki tells TMZ Sports ... noting, "I'm so grateful for my health."

Nikki says the diagnosis -- along with her neck injury -- will most likely keep her out of the WWE ring forever ... but she believes in miracles and hopes one day she can return to wrestling.

"You never know ... we'll see what the man upstairs has in store for me."

In the meantime, Nikki says she will monitor the tumor for the rest of her life "because you never know how it can change."