I think it comes down to two things. How sensitive your brain is and which of the meds.

I remember many, many years ago reading my med book, this was when SSRI's started getting popular. And it seemed like some SSRI's caused downregulation (mainly not in the serotonin system but the norepinephrine one) and some didn't. I recall Zoloft caused a severe downregulation while Celexa caused none. These were very early studies so I'm sure this has been updated many times over, I don't know what today's science says.

I wish it would only take me a few months to go back to normal, I sort of took for granted my brain was going to repair itself, but after three agonizing years, I gave up and went back on meds.

In animal studies, they overdose baby rats on antidepressants to make them depressed, to study depression. I wonder if I sort of have an immature brain (being autistic=said to resemble a childs brain), and that my med sensitivity also played a part. They thought back then it was safe to put exactly anyone on the max dosage and they did that with me, they didn't even know some people could be sensitive.