I have had parts take too much of a prescription also. And realized it afterward.

What I do?
-it is a shout for help or attention not a serious suicide attempt
-get over being upset about it
-that part is in pain
-ask who is hurting and why
-listen
-be curious
I've done this with the help of therapists most of the time. I usually feel a need to confess what I have done and I would rather tell the therapist than a doctor. And in the meantime, I continue to work at building trust, affection, acceptance, love between parts. I think that this is the eventual cure.