ADHD and autism both fall under the umbrella of neurodiversity, which refers to variations in the human brain and cognition. As most neurodivergent (ND) conditions are neurodevelopmental (affecting the structure of the brain as it develops through childhood and adolescence), they do not disappear with age and affect people throughout their entire lives, not just childhood.
Stimming or fidgeting is therapeutic and essential for neurodivergent brains, and there are multiple reasons for this.
One such reason is that neurodivergent individuals can react to sensory stimuli such as noise, light, texture, or other environmental factors in different ways than neurotypical people might. (Neurotypical referring to anyone not affected by a conditional classified as neurodivergent). A common shared trait of neurodivergent conditions is an inability to regulate your senses, so something as simple as noise from a fan could potentially be overstimulating. Stimming or fidgeting is controlled self-stimulatory behavior and can help neurodivergent people manage potential sensory overload and ground themselves.
In addition, any amount of physical activity, even simply using a toy in your hands, can lead to increases in norepinephrine and dopamine. These chemicals are naturally found in your brain and sharpen focus & increase your ability to regulate your attention. Neurodivergent brains frequently have a deficit of these chemicals, so their ability to focus or regulate attention can be hindered. So as a result, stimming or fidgeting can help neurodivergent people increase their focus and attention regulation capabilities.
Besides using stim or fidget toys, what are some other common ways that people stim? Some common examples include pacing, twirling your hair, picking / biting your nails, rocking your body back and forth, or rapidly moving your hands also known as flapping.
It's something that neurodivergent people have a physical need to do, and so when they are prohibited from doing so by a school, workplace, or other institution it can be very distressing.
If you're interested in learning more, there are some excellent resources online that extensively cover the topic. Here are a few examples that helped me write this page!