I'm not high functioning but I'm often perceived as such. I rarely leave the house, I cannot work or study, cannot manage independently or take care of myself. I rely on others to just about get by.
However, I conceal my physical and emotional pain very effectively in public and in the presence of other people. I don't leave the house much but when I do, the vast majority wouldn't know that something is wrong (unless I'm in too much pain to move). Even when I'm in agony, I don't complain, I don't cry, I hardly even grimace. The same goes for emotional pain. Previous psychologists and therapists have commented on this - even they couldn't pick up on the underlying anguish because it's that hidden.
I acknowledge the advantages of being able to mask my struggles so well. However, there are definitely drawbacks to this too, such as not being believed, not being taken seriously if I communicate my struggles, not being listened to or supported and everyone assuming I'm fine, even if I'm explicitly telling them otherwise. These difficulties aren't exclusive to people in my position, of course, but it makes me easier to ignore and brush off. Especially for health and support services.
The capacity to remain unwavering and unmoving in duress is an ability I learned due to long-term abuse starting as a young child. Being openly vulnerable has proven to be unsafe over and over again, so I had to wear a convincing faƧade to protect myself. Despite this awareness, I can't discard it even when I want to, when it directly works against me. Even if I'm internally screaming, I am outwardly smiling.