There are few viruses that can damage hardware IRL. Most tend to target the thermostat or fan controls. That is a real thing, and it has even been used by the CIA to target Iranian nuclear reactors. Computers produce a bunch of heat, and if they overheat, they break. The principle is the same as why you shouldn't run a machine gun until the barrel is red hot, because that increases the rate of failure. The circuits in modern PCs may be tiny, but they are still conductors of heat and electricity. Heat them too much, and Bad Thingstm happen.
Yeah, and imagine what could happen if you had a virus that targeted a bunch of power supply controllers at once, and that were coordinated. You could potentially do crazy things like having all the computers reboot at once, and set up badness in the power grid (think about all those cascading power grid failures -- now, imagine if you had a few million machines in a botnet you could change the power levels on at will, up to and including rebooting them!).
The idea that a Crash virus could affect hardware that is busy piping a signal to all your biological inputs that makes you have a seizure of some kind isn't crazy at all -- think of epileptics, who can seize in response to strobe lights. Or how about a heart attack? Well, if you can scare people enough to get repeated adrenaline spikes...
Well adrenaline alone probably wouldn't do it... tbh, given the prevalence of datajacks and simrigs your best bet would probably just to send a fairly decent whack of amps in to somebody's body to send the heart into fibrilation, you'd probably burn the thing out in the process (most of the circuits in a simrig probably aren'treally designed to handle that kind of voltage but you wouldn't need long... and it's not as if hardware preservation was high on the list of priorities for the crash virus), see the thing is that biologically speaking the heart is pretty resillient: although heart rate is modulated by a variety of factors the heart muscle itself is capable of contracting on its own. There's a small region of tissue called the sino-atrial node which acts as a pacemaker for the heart, but even if you burn it out (and in fact this is occasionally done today to deal with certain risky arrythmias) the heart will continue to beat at a rate of approximately 40 bpm on its own. Now that's not enough to maintain any sort of real activity (even getting dressed would be exhausting) but it *is* enough to maintain basic life support. I'm more inclined to think that the crash virus would go after the brainstem: matrix gear is already designed to interface with the brain and shut off bits of the brainstem and you could eliminate somebody's respiratory drive, whack the Reticular Activating system and somebody could literally go to sleep and not wake up (it's involved in modulating sleep-wake transitions and so forth, as a consequence take it out and you'll not only go to sleep but you'll lose the ability to come out of sleep unless somebody plugs some electrodes in and manually stimulates it.
But this is a minor quibble, in short, yeah what the Crash virus did to people is sci-fi, but not so incredibly sci-fi that it's unbelievable, there are pathways it could take to create at elast some of the effects it's descirbed as doing.