I find this slightly odd - there are two forms of "ceterezine" - ceterezine hydrochloride, and ceterezine dihydrochloride (there are probably others, but I only know these two). I wonder if the warning is a blanket covering all forms but I would have expected clearer wording.
Personal experience is that I'm ok with the hydrochloride form after the first couple of days of being grouchy & irritable (so nothing new there!) but that the dihydrochloride knocks me for six. In fact I was originally prescribed the hydrochloride variant to stop all of those side effects. The rest of my family all react the opposite way around.