Definitely gotten 'jittery' from over vaping 24 mg nic. Very similar to the feeling when one drinks too much coffee over the course of a day. Would load up a tank with 24 to take to work for smoke breaks since I couldn't vape all the time while working and would wind up vaping it at home after work in my normal chain vape fashion. Would keep me up for hours when I really needed to just stop and get some sleep. Finally decided to just drop the nic down to 12 and deal with any cravings that popped up at work with will power. Surprisingly didn't find much of a difference. Jittery feeling went away and I can go without vaping for hours now if I have to.