Christ! This sounds awful honestly. I never get personally how some people can just binge on cocaine for days, personally there comes a point for myself where more cocaine just prolongs the bad feelings.
This is a commonly repeated idea but I am not sure that there's actually any evidence that "confusing the parasympathetic nervous system" is a real danger in itself. The dangers of mixing downers and uppers typically relate to accidentally dosing too high with one because of the masking effects of the other. And of course, cocaine and ethanol is a special case because of the toxic cocaethylene metabolite. However benzos, on the other hand, as far as taking other substances to combat uncomfortable or even dangerous reactions from too much cocaine - can be considered, probably, one of the least harmful options. Benzos have a very wide therapeutic index and most of the commonly prescribed ones do not typically depress breathing too much except in extreme doses, or mixed with other downers, and essentially all of them have a far longer duration than cocaine, so will typically outlast any excess stimulation from the cocaine.
Of course, the absolute best HR option is to not do so much cocaine in the first place

... but on the basis that it's already too late for that, taking a benzo is not the worst option if you're in that anxious, awful place where it feels like you're fighting off a heart attack, and as long as you're not planning to do any more cocaine.