What is the worst psychological torture you can imagine suffering?  

There are a lot of horrible things that can happen that can mess a person up in the mind. The one that you mentioned is the obvious one. It is even worse if you see it happen and while you know that there was nothing that you could have done, you sometimes wonder if you could have done something. That could be something that could be horrifying.

I think being captured by someone would also be a lot of torture. I have this horrific scenario that actually did happen in a nightmare that I had many years back. I was tied up, which could be bad enough on its own. However, I was blindfolded, gagged, and my ears were covered. Now that seems like a scary existence. You have no sense of what is going on around you, no sight, no sound, you cannot talk and you cannot move. That would cause even the sanest person to go completely mad after a while.