Are these withdrawal symptoms caused by reinstatement?

[panic_down_under]

after 2 terrible nights and days I upped the dose to the original starting dose of 7.5, with the thought that, I can take my time again to taper but in a much slower pace. And I’m fine with that.

I don't think tapering slower would have prevented the insomnia from returning. You were only on mirtazapine for a short time at a small dose and took almost nothing for over a month without insomnia returning so I don't think this is a withdrawal issue. I suspect the insomnia is a distinct problem of its own, or maybe a sign of a deeper issue, anxiety, depression or something else. But your doctor is in a better position to judge this than I am.

Did your psychologist show you ways of handling anxiety and insomnia, or was there just an expectation that after a few weeks on the med things would have simply settled down and no longer be a problem?

I have been sleeping well since 4 days so that’s great! but I often feel very sad during the day, for no apparent reason. I also cry a lot and feeling a bit dizzy.

Are these withdrawal symptoms caused by reinstatement? Or could this be my “original” depression?

I can't say. It may be a return of whatever was triggering the insomnia, or it could be just side-effects from restarting mirtazapine. I think you need to discuss this with your doctor and/or psychologist.