I've gotten a nic overdose twice from chain vaping (different strengths) and I believe it is caused by the lower absorption rate. If you're used to smoking, your body knows instantly upon inhale how much nic it has taken in. With gum, patches, vaping, or other methods, there is a delay and you can vape too much during that delay.
Once I get the anxiety, I get a craving for a cigarette, and of course that will make it worse. So I keep some 0 nic around and vape that until the anxiety is gone. It's the 61-year-old's equivalent of sucking my thumb I guess.
Now that I've started using WTA eliquid, which contains OTHER alkaloids also found in tobacco, I find I get satisfied BEFORE I get anxious, so that works to prevent over-vaping.
Back when I was studying in college after the kids went to bed I did the same thing with caffeine and learned to go from caf to half-caf to decaf to Postum over the hours, to keep my alertness up by the flavor but not become anxious from too much caffeine. If you get some good 0 nic liquid, you should be able to do the same thing with your vapes...taper down during the course of the evening, and switch to entirely 0 nic if you get anxious.
Both times I got the anxiety issues, it also helped a LOT to eat something a bit heavy, and send the blood to my stomach. No idea why.