Meet Julie McGovern.
The student from Arkansas has long been physically active, running on her high school and college track teams. But after experiencing headaches, and excessive tiredness a doctor told her she had mononucleosis, which meant she had to curtail a lot of her sporting activities.
Sadly, six months after her mono diagnosis, Julie was still suffering from migraines and extreme weakness - even walking to the postbox would make her out of breath. After searching for an answer for months, eventually Julie learned she has Postural Orthostatic Tachycardia Syndrome (POTS), a chronic and debilitating illness which can make it difficult to even stand up as the body can't adjust to gravity very well.
Understandably, POTS has had a devastating effect on Julie's life - but one of the hardest things to deal with is the fact that since she has no physical symptoms, people often don't believe she's ill.
In a post on Facebook she wrote:
Being a young person with an invisible chronic illness is one of the hardest things I've ever dealt with. People think I look fine, so I am not sick. It isn't that I'm looking for sympathy, but respect and compassion. It has been an incredible odyssey going from a vibrantly healthy person to someone living with a chronic illness.
I am unable to keep up with my friends and my pride often keeps me from asking for help. Sadly, the disbelief of others around me has caused me to remain silent about my illness. It is like I am being punished for being sick.
Bit by bit, Julie is learning to adjust to life with her illness. But she was dismayed a few days ago to come back to her car and find her "worst fear came true" when somebody left a note accusing her of faking her disability on the windscreen:
So many emotions flooded my mind. I was hurt, I was angry, I wanted my voice to be heard, but this person is a coward and could not tell me what he/she thought to my face...
This person doesn't know me or my struggles. They don't know what this illness has taken from me. They don't see the countless nights I cry myself to sleep, soaking my pillow with tears, pleading - praying for God to heal me. They don't see the weakness, the pain, the symptoms that are very real, but only I can feel. They don't understand, and until it happens to them they never will.
But Julie refused to let the anonymous note affect her self-esteem and her determination to live life to its fullest despite her chronic illness, and took to Facebook to write an impassioned open letter urging people to remember that illnesses come in all shapes and sizes.
Today my illness was invalidated, but it doesn't make my illness any less real or my fight any less important. I will continue to park in the handicap spot and I will raise my head high and continue to join the fight in searching for a cure.
Since being posted last week the note has been shared online hundreds of times and it's triggered an outpouring of sympathy and support for Julie's experience.
Julie told i100.co.uk that there has been both positive and negative reaction to her post, but she's happy that the conversation has been started.
She's received hundreds of messages from all over the world thanking her for her courage in standing up for herself, but she said it was about more than just her.
"I am so sick of fighting against all of those who say our struggle isn't true, when we should be putting our energy into fighting for a cure - fighting for the quality of our lives. This is why I used my voice," she said.
I believe it is making a difference, and even if it is a small difference, at least it's a little better than it was before.
Read Julie's post in full here.