Basically your body/brain has to get used to it again. All antidepressants have start up side effects. They often start out strong when you first start taking the med (and a med you once took, stopped and started again is like a new med to your body again and it has to get used to it all over again). Those start up or transient side effects often get less and less as time goes on until the 6 to 8 week mark when your body has the drug on board and is used to it. There still may be some side effects from the medication but they aren't usually like the start up ones. It's up to you though if you can tolerate how you are feeling. It's interesting that the first time you took it, you didn't have the same kinds of start up side effects.
Is it a generic drug you are taking? I've found that each generic med can be made by a different manufacturer and each may be slightly different. Usually the difference is subtle but from one month to the next even, you can get slight differences with a chronically taken generic version of a drug. So, that's a thought too.
You should check in with the doctor that prescribed them. Perhaps you can go to a lower dose and titrate up more slowly in dose or you may decide that this time around, this isn't the best choice for you if you are too uncomfortable. Let us know what you think!
Yes. Brains are complicated things and these drugs are just odd in how they make them work. Often, people find that when they take an antidepressant for a long time, stop, and try it again, it doesn't work at all the second time around. Or like you people get different side effects. Anxiety can make us worry a lot about taking meds if that's where the anxiety is focused or if we had a bad experience, but I don't know that the particular experience of brain zaps is something anxiety can create. It's so tied in to withdrawal from antidepressants particularly those that focus on serotonin. Who knows what's happening? Could be your brain is just very sensitized to the med now. No real way to know, but if you manage a system that stops you from missing a dose and this stops happening, you'll know it's from missing doses. These drugs are funny -- I had the worst withdrawal perhaps in the history of withdrawals and never once had a brain zap. You just don't know with this stuff.