Bella Hadid battles "severe isolation and depression" whenever her Lyme disease symptoms flare up.

The 29-year-old supermodel has opened up on the mental struggle of dealing with the disease on a longterm basis after being diagnosed with the tick-borne illness in 2012 - admitting she feels devastated every time she's dealt a setback.

In a post on her Instagram page, she explained: "I wish it wasn't so intimidating and difficult to explain the pain/ exhaustion/ fatigue,/ anxiety/ brain fog insecurities that come with chronic illness / co infections/ mental health/ trauma etc.

"Leading to severe isolation and depression, especially over long periods of time. Especially when you try anything you can. You learn about your symptoms, read books, read other stories, try to self diagnose when you demand answers that no one can find.

"You fight. You finally have a few good days. You think you've found the right protocol, the right routine, the right treatment ... and then a flare up comes back and all of a sudden nothing feels certain again.

"Back to cancelling plans, back to the inability to make decisions because you never know what you are going to feel like from day to day."

Bella added of her symptoms: "You wake up with anxiety already living in your body. Physical pain before your feet even touch the floor ... And somehow, still have to find the strength to move through another day in a body and mind that are completely exhausted.

"Sometimes it feels like unless you've lived something like this, or loved someone who has, it's impossible to fully understand ... "

However, she ended her message on a more positive note, adding: "There is light, even if you can't see it today ... There is hope.

"As so many have said. I have to remind myself that healing isn't linear ... I believe God puts before us, somehow, only what we are capable of carrying, even when we don't understand why at the time ... [there's a] deeper purpose to all things in life."

She concluded: "Every hardship leaves us with a lesson, a deeper compassion, or a strength we never knew we had ...

"It leads us to the places and people and experience we have now. I have so much gratitude for life, but without living in a body that has more rough days than good.

"It's hard to find joy or purpose or reason to even go outside ...but we will keep trying! always!"