The reason is that serotonin per se isnít causing any of these conditions. Rather, itís either inhibiting or allowing them to occur. Serotonin turns out to be a general inhibitory neurochemical. When itís high it tends to generally inhibit behaviors; when it drops it stops doing this.
I read the article again and this part was interesting to me personally. I suffer from derealization, it was pretty bad almost 5 years ago when it first started, but months afterwards it got manageable and now I don't really notice it, although I still have that "feel" of it lingering in my brain.
But what I noticed back then is that after a good night of sleep it pretty much disappeared and it got to its worst point before I went to sleep, specially if I didn't sleep well the night before.
I wonder if it what due to changes in serotonin levels? Haven't tested this out through diet changes though.