you probably got a kernel panic, which froze the system. it’s like a BSOD on windows, except on linux, there isn’t a proper stack to handle them when they happen while you have a graphicam session running, so it kinda just freezes
i don’t think reisub would do anything, because the kernel was probably already dead
you don’t risk corrupting much data by hard-reseting your pc on linux – journaling filesystems, like ext4 or btrfs, are built to be resilient to sudden power loss (or kernel crashing). if a program was writing a file at thz time the kernel crashed, this one file may be corrupted, because the program would get killed before it finished writing the file, but all in all, it’s pretty unlikely. outside of fs bugs, which are thankfully few and far between on time-tested filesytems like ext4, you shouldn’t have to worry much about sudden power loss!
unfortunately, figuring out the cause of these issues can be challenging – i’ve had many such occurences, and you have no logs to go off of (because the system doesn’t have time to save them), so you’d most likely need to figure out a way to send your kernel logs onto another system to record them
as general mitigation steps, you should try monitoring your cpu temperature a bit closer - it could be high temperature tripping the safeties of your motherboard/cpu to avoid physical damage to them - in which case, try installing a daemon to control your cpu frequency, like auto-cpufreq, or something like thermald specifically made to throttle your cpu if it gets too hot (though i think that one is intel specific)