Overload is hard to describe to somebody who doesn’t experience it, because it’s not simply the physical pain from something being, say, too loud. Its effects run much deeper.
Some days I can cope with my sensory environment better than others. I know fatigue lowers my threshold of tolerance, but it goes beyond simple intensity–brightness or loudness for example. Other qualities of the sensations play a bigger part than is generally realised.
With sound, for example, I can handle music and sounds that are rhythmic much better than the chaotic variations of speech. I struggle listening to a person speaking when there is background noise but have no problem at a big rock concert.
One big difference between the two is that with music there is a much lower cognitive load because I’m not trying to focus on the words and put meaning together. Instead I experience it at a more basic, emotional level without the need to process language–I don’t generally focus on vocals other than as just another instrument.
Overload affects my brain as a whole: if I’m struggling with sound I close my eyes to reduce the amount of input I have to process. I mostly stop talking and moving, all my effort going into handling the incoming sensations.
I generally know that I’m approaching a sensory/cognitive overload because my tinnitus becomes intrusive, I struggle to understand what people are saying, light becomes painfully bright, hurting my eyes, and noises feel as if they are stabbing into my head.
It puts me under a considerable stress, and it can take a long time to recover. During that time I have to reduce my sensory load as much as possible: preferably find a dark, quiet place to sit or lie down.
I do wonder whether age is a factor too because as I get older I’ve found I can’t cope nearly as well with a “busy” sensory environment and I get tired and overloaded much more easily. I think that’s a thing in general with ageing: we injure more easily and it takes longer to recover.