How to Talk to your Parents About Seeing a Therapist.

I feel like I'm depressed and maybe suicidal? I don't know. I haven't attempted suicide but I've come close and I have a plan for if I were ever going to do it. I want to see a therapist because it's becoming too much for me to handle on my own but I don't know how to approach my parents about something like that. I'm only in high school so I'm afraid they won't take me seriously.