If one of my friends said they were going to the bathroom and was gone for 30 minutes, I wouldn't go looking for them or mention anything. The details are usually too rude for public conversation, and generally the person prefers some privacy. There are also any number of other reasons that you could have chosen to leave and were just using the restroom as an excuse. If that were the case, then it would have meant you didn't want to talk about the real reasons you left, so it would be kindest not to ask.

30 minutes isn't very long. When you were gone for longer, they did ask. You also obviously weren't kidnapped in your own house.

I would absolutely not confront your friends about this. If I found out that my "friends" were giving me secret tests and judging me when I failed, then I would be pretty put off. This was irrational and it does happen sometimes to people with mental disorders. However, it is incredibly unfair to your friends. The real issue here is the path your mind took in this whole thing and what it led you to do. I would focus on addressing that.