I don't know about the 'don't care about anything' part - but there's some speculation out there about a "one shot theory" where some people can't handle the psychological impacts of a ayahuasca trip and their brain is scrambled by that 'one shot' and they're never the same.. a number of relatively normal people who do a retreat don't really come back all the way. Combined with the frequency of later onset schizophrenia and while life might feel pretty stable for a middle-aged person, your mental ability is more precarious than most people think.