Chronic illness is a tricky thing to deal with- both physically and emotionally.
Illness is always a challenge- whether it's a small challenge e.g. a cold, or a bigger challenge of something like pneumonia. Any reduction in health affects quality of life. It makes us suffer to some extent. Sometimes they make us consider our mortality. Sometimes they complicate things a little or a lot by meaning we need to take medications or look after ourselves more. All of us have experience of illness of some degree. A minor acute illness will probably cause few disruptions and normal life will resume very quickly and will just necessitate a few days taking things easy, feeling a bit under the weather. A major acute illness will normally mean a few trips to the doctors or a short stay in hospital with some aggressive medical treatment to make the person better; people normally rally round the sufferer, there's lots of support and an understanding that things are bad, but recovery normally comes around quite quickly.
Chronic illness is a totally different matter. It challenges the individual and the people around them on a completely different level. With a chronic illness the problem doesn't stop, the end simply isn't in sight, and by definition a chronic illness can't be cured- there isn't a 'quick fix'. Some chronic illnesses can be successfully managed and brought under control with medical treatment or lifestyle management but many others can't, the symptoms simply don't stop. Not getting a break makes the situation all the more difficult to deal with. If you knew that one day a week you would get a day of respite to do things and have a break from the pain and suffering it would make it a lot more bearable, but that's not how chronic illnesses work.
Physical disabilities (excluding chronic illness) such as the loss of a limb etc are different again. There is no constant illness, often no ongoing symptoms. People can see and understand your problem. Doctors can't make it better but you can make the necessary adjustments in your life and things are predictable. I admit I have no experience of this type of disability and I'm sure it's not easy to have limitations with absolutely no prospect of them going away, and everyone seeing and knowing that you are disabled and have health problems must bring its own problems in terms of employment and how you are treated by society. There is the advantage though that you can plan ahead, know what you are capable of, work out ways around things and people are more aware of the type of help you might need. Lots of people with these sort of disabilities can achieve great things- just look at those in the Paralympics and the constant news stories about double amputees climbing mountains and walking across the North Pole etc. There is the expectation that disabilities should be defied.
These sort of disabilities are similar to chronic illnesses in several ways. They force limitations on the sufferer or mean that things have to be done differently. Most will require medical appointments long-term. There are emotional challenges with both due to changes in lifestyle, limitations and differences in your body and the way you view yourself and others see you.
Chronic illness is also different though in a number of ways- it's more unpredictable. There is physical suffering and there are ongoing symptoms. There isn't the option to battle against your situation, seem heroic and achieve amazing things. There were very few chronically ill people in the Paralympics. Those with significant chronic illnesses don't climb mountains. Our achievements are far more ordinary. Chronic illness sufferers win battles every day but they are small things- walking a bit further than normal, staying standing without feeling sick and dizzy, sitting up for longer after a relapse, managing a whole day at school/Uni/work- things that healthy people wouldn't consider an achievement at all. Our achievements certainly aren't worthy of TV news stories or newspaper headlines but we are also pushing our bodies to the limits and achieving the best we can- our limits are just very different.
I don't mean this to make us sound brave, and I'm not saying it to get any sort of recognition, I just think chronic illness is largely forgotten by society. We don't get the publicity that most visible disabilities get. We're disabled but we're also ill. We do have to 'learn to live with it' but its difficult when you have symptoms every day that constantly change. If you had an ear infection one week, a chest infection the second week and constant migraine the third week and food poisoning the fourth week would you get to the end of the month and say it's fine because you're used to being ill now? I doubt it.. You do adapt to the level of pain you're in and get used to the other symptoms to some extent- but it still hurts, you still feel ill, you still notice the twitches and the cramps and the nausea and the weakness. You do have to learn to accept it but there's a constant grieving process with every loss, and every relapse brings about new losses or highlights previous losses and the grieving process starts again. Acceptance, the final aim of the grieving process, is only ever a transient thing- everything seems easier when you're able to accept your 'new normal' but you never know how long the stage of acceptance will last before the cyclical process begins again and the feelings of loss, unfairness and frustration prevail.
Most people with chronic illnesses- CFS, lupus, MS etc- look relatively well. There are few signs that the person is suffering. It's therefore important not to judge anyone by their appearance. Don't assume someone is healthy just because they're young. Don't expect someone to leap up and offer their seat because they look healthy. Be considerate to everyone- you never know what battles people are facing.