I wouldn't assume it's a bluff; I once came home from college later than expected with a dead phone and the paramedics were there because a parent had in fact had their first ever panic attack and thought they were dying. (There were extenuating life circumstances and we worked things out, I'm 100% sure that one was not a bluff or manipulation and suspect I would never have heard about it if I'd come home a bit later.)

But treating it as if it's not a bluff works fine either way; react by being genuinely worried for their health and refuse to discuss anything other than whether they've seen a doctor about it.