"The Big Bang Theory" star and comedian Kate Micucci is battling lung cancer, and says her diagnosis was a total shock because she's never smoked a day in her life.

Kate shared her scary medical news over the weekend, telling folks on TikTok she had surgery to remove her lung cancer and is recovering in the hospital. Thankfully, Kate says they were able to detect the cancer early.

What's most puzzling to Kate is the fact she's never smoked a single cigarette, but still wound up with the illness. However, she's keeping a positive outlook on the whole situation, given the surgery was a success.

Smoking is the leading cause of lung cancer -- but, about 15 percent of cases are linked to other factors such as secondhand smoke, asbestos and various chemicals ... according to the World Health Organization.

She kept a smile as the vid went on, walking around the hospital with the help of staff right behind her ... and she even posed for the camera with her typical hospital food -- a small box of cereal and a banana!

Fans of "The Big Bang Theory" remember Kate playing Lucy in a handful of episodes, who was Raj's love interest.

She's got credits in tons of other projects ... including "DuckTales," "The Little Hours," "Garfunkel and Oates," "Raising Hope," "Steven Universe," and she's played the voice of Velma in "Scooby-Doo" since 2015.

She's also married and has a 3-year-old son with husband Jake Sinclair ... who's written and produced tracks for musicians like Taylor Swift, Weezer and Panic! at the Disco.