A friend of mine who suffers from depression once made the comment that "when you have cancer people line up to help you but when you have a mental breakdown they run in the other direction." Sadly, this is true in my experience too. Many people don't get how hard it is for patients with chronic conditions that have symptoms that don't present the same way as more well known conditions or diseases like cancer or a broken bone.
Another person I know suffers from a chronic condition that causes extreme fatigue. After months of struggling with the condition this person took a medical leave of absence from work. While off from work they sought new treatment options and began extensive resting in the hopes of making a full recovery. Unfortunately when telling friends and colleagues about the medical leave several people made comments about how nice it must be to have paid time off to lay around and do nothing. People have suggested this person should write a novel and "enjoy the vacation". These types of comments are not just thoughtless and rude, they can be destructive.
Most people simply do not understand how difficult life is for people coping with a chronic medical condition or recovering from surgery or injury. This is especially true for people who suffer from forms mental illness, fatigue or chronic conditions. People often make comments that the patient "doesn't look sick" or suggest overly simplistic solutions such as exercising more or cutting caffeine out of their diet. Unfortunately some people feel that in order to be "legitimately sick" a person must look sick in a particular way. This is ridiculous and infuriating. This is because the underlying message in these comments is that the patient is simply being lazy or exaggerating maybe even faking their symptoms.
If you find yourself dealing with a chronic condition that people often misunderstand it's important to find strategies that help you cope with these types of comments. While there is not a particular formula or step by step plan that works for everyone, I believe there are some effective strategies for coping.
First I strongly recommend you connect with others who are coping with your same condition. Ask your physician or other medical providers if they can suggest a support group or other resource for meeting others with your condition. You may also be able to find online groups with others with your condition as well. You will be able to learn many things from others who are coping with the same problems including ways to easily explain facts about your condition to others.
Second, it is important to "choose your battles wisely" when it comes to getting others to understand your situation. Think about who the person is and how relevant it is to you and your life if they really "get it" or not. If a co-worker whom you rarely interact with makes a comment that shows they clearly don't understand the reality of your situation it probably isn't worth the effort to explain things to them. However if your immediate supervisor or a team member doesn't understand it is important that you educate them since you will rely on them to support you. I know it can be infuriating when people say thoughtless things that minimize your condition but letting it go and focusing on the people and things in your life that really matter is a more important use of your limited physical and emotional resources. You don't have to be an ambassador to the world explaining the legitimacy of your condition. It's only important that the people who interact with you most understand it.
I know it may be hard sometimes to just let it go when people make thoughtless comments about your condition. Sometimes it will make you feel better to explain to them why their comment is unwelcome, uninformed, or otherwise inappropriate. It is fine to let people know. It may be useful to have articles or resources that explain the facts of your condition available to send to people when they make comments. This can make it easier to explain it. At times you may find this empowering and validating to have this conversation with someone, even if they are a stranger or distant connection. It depends on your feelings at the time.
There is not a formula or simple way to know the best way to handle each thoughtless comment you get from people who just don't understand your condition. Sometimes it will make more sense for you to reply with cold stony silence and a glare, sometimes you may ignore it, sometimes you may explain. My recommendation is that you do what is most empowering to you in the moment. Recognize that your most important responsibility is to your own self care and well being and act consistently with what supports it.