Neurodivergence

It's a case of levels. ADHD and autism sit well along sliding scales.

ADHD is caused by under stimulation he brain. The brain can't keep it's own dopamine levels high enough levels, and so relies on outside stimulation to do this. Boredom isn't a mild feeling, it's more akin to a crack addict in withdrawal. Unfortunately, our fix is novelty, which has an unfortunate shelf life.

On another scale is Autism. This (amongst other things) can limit our sensory bandwidth. We can only cope with so much sensory information at once. This creates a bias towards stable predictable patterns. They are our crutches. Excessive novelty is like taking away an amputee's crutches. They can often still walk, but it's a lot harder, and more painful.

For both of these, the overhead capabilities can vary significantly. Most of the time, we can find a useful balance. It's like a venn diagram, with 2 circles, we need to remain in both. Unfortunately, on bad days, those circles shrink. This can force us to choose, when they no longer have an overlap (at least one we can reach). Do we choose stability, and have a screaming, tantruming toddler stuck in our head. Or do we satisfy it with novelty, but walk the knife edge of complete sensory overload and/or shutdown.

For most people, those circles are larger and more stable. They don't have to choose which beast to feed, and which to be mauled by.

In short, both conditions push their sufferer close to the edge on a normal spectrum. When both are pushed, we can be completely fucked over by brain chemistry.