You can certainly stop breathing without anyone manhandling you - people collapse and stop breathing with no-one near them at the point of collapse in all sorts of situations (perhaps sports collapses would be the best equivalent - lots of exertion and then collapse and breathing stops a little while later). The whole excited delirium thing is not at all well understood. There used to also be something called SADS (Sudden Adult Death syndrome - an equivalent of Sudden Infant Death syndrome where there is collapse / death for no apparent reason) but I don't know whether that is still seen as a specific syndrome in it's own right or whether things have moved on. There ARE some statistical things becoming apparent about excited delirium - it appears to affect black males disproportionately, there seems to be some correlation with drug and / or alcohol use and there seems to be some correlation with mental illness ... but I have not seen specific, peer-reviewed research establishing any of these things for sure and there are, of course, lots of other reasons why some or all of these features may co-occur without there being any actual link. As I have said before, whilst we go into all these types of cases with a "the police have beaten him to death" conclusion in our minds from the outset we will never actually get to the bottom of what the causes actuallyare so that we can help make sure they don't happen again. In any particular case the police may have actually killed a prisoner by excessive use of force ... but that is only one of a number of explanations and, on the basis of the outcome of the enquiries which take place, a very unlikely one. More likely is that a careless or slightly excessive use of force in restraint has caused / contributed to death, or that lack of care and attention has controbuted to it, even though all use of force has been lawful and justifiable. Campaigners who immediately encourage families to go down the "beaten to death" route are not helpful.