"And then I was like, maybe it's not just a coincidence, maybe there's something actually medically wrong with me. So, I went to the ER after a very long day of work with lots of makeup on, and I just got home, from Friday night."
Despite doctors running "multiple tests" at length, there was "no scientific explanation" for her breathing issues.
She explained, "They ran multiple tests, multiple times, and there's nothing physically wrong with me. So, wonder why I was there."
Thankfully, the brunette beauty was in good spirits on Friday, taking to Instagram with a video of her dancing while hooked up to a hospital machine.
WATCH: Sarah Hyland dances in the hospital despite her illness
The cute video was a birthday shout-out to her friend.
She also took the time to take a gorgeous glam selfie
Unfortunately for Hyland, she is a frequent visitor to the hospital with various health issues. The star suffers from kidney dysplasia, a condition that means her kidneys did not develop properly when she was still in the womb. Because of this, Hyland suffers from painful cysts, which has led her recently to a second kidney transplant.
She also suffers from endometriosis, a painful disorder where the tissue that lines the inside of her uterus is grown on the outside. For this, she has also had multiple surgeries.
Because of these health issues, Hyland often gets down. Thankfully, her mental health has improved since she began dating boyfriend Wells Adams, 34.
At the time, she said, "He was texting me in the morning before I went into surgery, and we were FaceTiming the entire time I was in the hospital.
"He's seen me at my worst. He was there through all of that. I think that's why I feel the most beautiful in his eyes, because he still finds me beautiful after seeing all that."
We're wishing Sarah a speedy recovery.