Irrational fears and altered sense of danger - understanding the polyvagal system in Autism and SPD

Many autistic people, those with Pathological Demand Avoidance (PDA) and Sensory Processing Disorder (SPD) struggle with either irrational fears, or issues with danger perception. This is all down to the Polyvagal System. Here I look at what this is (in simple terms) and how it affects autism and associated conditions.