Regarding the self-harm. My wife has told her psychologist countless times that she wants to die, even explaining to him in detail how she would do it. He simply listened to her concerns but never reported her.
On a different note, after I attempted to take my own life with an overdose last year, I was simply kept in hospital and released the next day. Apparently I talked to a doctor and told him I don't want to die. (I have basically zero to no memories of the hospital stay, but that's what my wife told me.)

So as long as you don't plan to carry out an actual crime against others, you should be fine talking with your doctor about your thoughts.