Especially if you consider self-harm, it is very important to be honest with your therapist. Even if it leads to an extended stay in a psych ward, that's better than throwing your life away.

When my depression took over so hard that i was sitting in my room with a knife in my hand and pondering cutting open my wrists, instead i went directly to the psych ward and institutionalized myself for 3 months, until my medication and therapy made me stable enough to leave without danger. Without this step, i would probably not be here anymore and would have caused untold pain to my surroundings. It led to many happy memories in my life which i wouldn't have experienced.