I think the worst situation I've had is the fact that it's difficult or impossible for others to read my body language about when I am not feeling well, and also difficult or impossible (depending on the time and situation) for me to communicate this in words and/or in any degree of useful detail. (I can sometimes feel pain but not point to where it is for instance, and I also have trouble reporting pain.) This has resulted in a number of untreated ongoing health problems and brushes with death and such, so I think I would call this the most unpleasant thing.
There are a lot of other things that have been extremely problematic in the world I live in (difficulty going from thought to action, difficulty going from perception to thought, difficulty with using language to communicate) but none of those really bother me the way the above does even when they are at their most extreme. Possibly because I can survive as long as someone assists me with the things I can't do in that regard, but I do fear for my survival a good deal, no matter how much other assistance I get, based on that difficulty communicating bodily pain and discomfort.
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"In my world it's a place of patterns and feel. In my world it's a haven for what is real. It's my world, nobody can steal it, but people like me, we live in the shadows." -Donna Williams