Kate Walsh is used to playing a doctor on TV, but she recently had her own harrowing experience having a brain tumor removed.

The "Grey's Anatomy" and "Private Practice" alum is OK now -- the "small lemon" sized tumor in her head was benign, and they got it all -- but she shared her full story with Cosmopolitan.com. She also taped a hilarious (but still serious) health-care commercial with her fellow "Grey's" alum Patrick Dempsey.

Here's what alerted Walsh to seek treatment:

"My pilates instructor said 'hey, your right side is dipping,' and it didn't feel like I was off, but I looked down and could see it. Then when I was driving, I started swerving into the right lane. The exhaustion got to the point where I could drink five cups of coffee and still not feel awake or clear. And then around April, I started having more cognitive difficulties. It felt like aphasia, but it wasn't just not being able to find words; I would lose my train of thought, I wasn't able to finish sentences, and that was when I got really alarmed.

I thought maybe it was menopausal symptoms, because there are a lot of the same markers, but I really pushed to see a neurologist, I just had an instinct. I had to really advocate, because they don't hand out MRIs so easily, but I got an MRI and thank God I did, because it turned out I had a very sizable brain tumor in my left frontal lobe. And three days later I was in surgery having it removed."

Walsh told Cosmo how playing a TV doctor -- Dr. Addison Montgomery-Shepherd -- informed her real-life attitude to health care:

"It was the total opposite! You'd think that after playing Dr. Addison for the better part of a decade, where I spent more time on a hospital set than at my house, that I would feel somehow more comfortable, but I was such a little scaredy-cat. In the hospital, I felt like I might as well be six years old. My mother gave me rosary beads, my friend gave me a stuffed animal to go into surgery with... I played a real badass on TV, but when it comes to being a patient it's such a vulnerable experience."

She said the biggest thing she learned is to go see a doctor -- don't self-diagnose.

"We're all so socialized to try to self-diagnose, like 'I'll change my workout, I'll change my diet.' I'm very proactive and willful and independent, and in the past, even though I played a doctor on TV for years, I was not one to go see doctors very often, other than for my annual OB-GYN appointment. So for me, it was a really big wakeup call to do annual check-ups, and that's why I wanted to pair up with Cigna for this campaign. I love the idea of changing the framing around healthcare, and changing it from a reactionary thing — 'Oh my god, I'm sick, I have to go to the doctor' — to something more along the lines of preventive care. We should go get a checkup the same way we go to the gym, just preventively, instead of waiting for something to go wrong."

That Cigna campaign she mentioned includes this great commercial with her "Grey's" husband Patrick Dempsey (Derek Shepherd):
Kate Walsh said she took off work for about nine months, but when she returned she "hit it hard," including filming Netflix's popular "13 Reasons Why," the movie "Girls Trip," a play in New York, and a new film called "Self."

"Grey's Anatomy" returns Thursday, Sept. 28 at 8 p.m. on ABC. "13 Reasons Why" Season 2 is expected in 2018.

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