Everyone's body metabolizes the medications a bit differently on an individual basis. I won't go into details, but it just depends on each person's body dealing with a medication.

Note that I was told that the body interprets the medication as a poison, so that may be part of the reason the differences between side effects or no side effects.

I suppose it is better if the change was gradually beneficial, not at a drastic rate.

You have the insight to recognize that your therapist will be helpful in recognizing when the antidepressant dose is at your therapeutic level. Sorry, I can't be specific, but you should listen to your gut feeling and keep going to your therapist.