Stereotypic movement disorder
Stereotypic movement disorder (SMD) is a motor disorder with onset in childhood involving restrictive or repetitive, nonfunctional motor behavior (e.g., hand waving or head banging), that markedly interferes with normal activities or results in bodily injury. While stereotypic movements are common in infancy and early childhood, a diagnosis of SMD is made only when such behaviors are prolonged, intense, and cause significant impairment.
Source: Wikipedia — Stereotypic movement disorder (CC BY-SA 4.0)