Why did my dog try to commit suicide?

I doubt very seriously that your dog was trying to commit suicide, they don't think quite as we do. I imagine what happened was that your dog was curious about something and just wanted to get down to the bottom (doing it the best way he/she could figure out), the problem is they don't have the comprehension or sense of perspective that we do. For whatever reason, there was just no caution or fear that he could actually get hurt (or killed).