Unlikely to bleed to death while conscious. However, if the impact causes unconsciousness (highly likely from head trauma), a bleed-at-not-otherwise-concerning rate is going to be a real problem.

Humans need watchdog processors. Even if we have to build them and add them. Something which watched your vitals in the background and alarmed when they became critical would be great.

"Heart attack" was probably someone extrapolating from "middle aged guy dies during exercise". Unless you actually had M.E. information beyond that, the natural assumption would be heart attack, and you'd be right 90% of the time.