People with intellectual and developmental disabilities (IDD) and autism are often marginalized and further traumatized because of behaviours that are difficult (challenging) for care providers and services to manage. These behaviours are similar in many ways to responses of our autonomic nervous system when triggered by danger and life threat – namely fight-flight-freeze (FFF) and shutdown survival responses. This discussion paper, drawing on polyvagal theory understanding, explores these similarities further from Outside-In (i.e., as observed and reported by others such as carers and clinicians) and Inside-Out perspectives (i.e., as described by people with IDD and autism engaging in these behaviours). Polyvagal theory, developed by Dr. Stephen Porges, explains how the sympathetic nervous system and the dorsal branches of the vagus nerve are involved in FFF and shutdown survival responses; the ventral branches of the vagus nerve are involved in the capacity for social engagement and in the experience of feeling safe. In our paper, the experience of feeling safe is investigated and triggers that alert the nervous system to danger and threat are identified. Being safe and feeling safe diminishes autonomic nervous system reactivity and automatic survival responses. We conclude that imbuing a safe experience for people with IDD and autism (from their perspective), through optimal health and supportive emotional and physical environments adapted to unique needs, will diminish autonomic nervous system reactivity and dysregulation, which in turn will diminish consequent distress behaviours that services and care providers find difficult. Being safe and feeling safe, are key to both treatment and prevention of emotional and behavioural distress and difficult behaviours.