If you over dose nicotine by vaping, your body will tell you. Youll get lightheaded, dizzy, nauseaus, maybe a little cold sweat on your forehead. This usually wil cause someone to put the mod down for a bit. These effects thankfully wear of fairly quickly. As natasha pointed out, wearing 2 time release patches meant she was getting a steady dose of nicotine that was only controllable by removing the patches, and if someone is having more serious symptoms, such as those she described, being able to think clearly enough to remove them was much more difficult to do than simply putting your mod down for a bit to let the nic wear off.
I completely agree with you, but... at times when I've intentionally vaped quite a lot of nicotine I noticed not just the immediate signs you describe, which do go away pretty quickly, but also as the day wore on a somewhat different set that seemed to have more to do with cumulative intake and didn't wear off so quickly. I'd compare it to having had a bit too much caffeine over the course of a day, not so much in its exact effect, but in its nature.
If I drink too much coffee over the course of a day I might be jittery for a while after the last cup, but I'll also feel sort of drawn for the rest of the day even after the immediate effects of the caffeine have worn off. Kind of like wearing the One Ring for too many years, and feeling like not enough butter spread over too much toast. But not quite as serious as that, I imagine...