14-year-old Lilly was diagnosed with arteriovenous malformation (AVM) when she was six years old, a rare condition that typically appears in the head, neck or spine.
AVM is found when there's an abnormal connection between arteries and veins, and can cause swelling and life-threatening nosebleeds to occur.
When Lilly was eight years old, she decided to launch a YouTube channel to raise awareness of people with 'visible differences' such as her own, and to create videos on a variety of topics, such as beauty, music and baking.
Having accumulated more than half a million subscribers on the video-sharing platform, the vlogger has recently taken part in a TV programme called My Life - I Will Survive, which is being aired on CBBC on 11 February.
While being interviewed on ITV's This Morning by Holly Willoughby and Phillip Schofield, Lilly spoke about being hospitalised last June due to her ill health, an event that has been documented in the TV episode.
"I was very poorly," the vlogger said.
"I actually ended up being emergency admitted to hospital because I was bleeding really profusely and they had to put me in a sleep-induced coma for eight days to stabilise the bleeding and just let my body rest really because I'd lost so much blood."
The teenager explained that she had then undergone surgery in August, in December and has another surgery scheduled for this summer.
Lilly described the period last summer as a "scary" time for her and her family.
With the exception of the surgery that followed her emergency hospitalisation, which Lilly wanted to keep private for her and her family, the YouTuber was happy for the cameras to follow her so that viewers could see both the highlights and hardships she experiences.
"I think it's really important to show the harder bits of life, because I feel like sometimes even with social media it can be a filter for only the good parts of life," she stated.
Lilly continued, explaining how social media can often make people feel as though they need to "purvey a perfect life", a concept that's highly unrealistic.
"Me living with a chronic illness, it is hard sometimes and I feel like some kids or even adults forget how hard life can be," Lilly added.
"So I wanted to show not only the more positive parts of course, but the harder parts."
My Life - I Will Survive with Nikki Lilly is being shown on CBBC on Monday 11 February at 5:30pm.