A skill may still be present even when it becomes harder to use.

Autism, ADHD, anxiety, rigidity, repetitive movement, sensory seeking or avoidance, impulsivity, social drive, and reduced danger awareness are genuine neurodevelopmental domains. They deserve direct support.

But a new or extreme behavior can also be the first outward sign that pain, sleep, bowel retention, hearing, airway, seizures, illness, heat, fatigue, puberty, medication, autonomic activation, or communication access changed. Severe teething pain preceded head-banging in one otherwise quiet young history. In a broader adult history supported by available records, sweating and breathlessness moved beside self-harm, aggression, and a collapse from sentences to sounds.

Neither example makes every behavior medical. Both demand the same sequence: define baseline, capture the change, test body and environmental candidates, support communication and safety, and record what returns. That distinction—capacity versus access—runs through every section that follows.