Downs people can be autistic too. My friend is part of a team that cares for a young man of twenty. He's severely autistic (and has the extra chromosome of Downs) His behaviour can be very challenging, as he has 'meltdowns' of agitation and frustration, triggered by noise, bright lights etc. He's a large individual, and there are always two carers with him. If restraint were needed (eg if Police were called, most unlikely!) they would probably use a light strap around the lower legs and handcuffs. One officer would always be in charge of the person's head, ensuring breathing isn't restricted and the neck is protected. (I've seen this method of restraint used twice, in Parkhurst Prison) For asphyxiation to occur, by fracture of the larynx or compression of the chest, it would mean an extremely poor, over-aggressive and negligent manner of dealing with the person.