Yes I've also had this feeling of impending doom a few times and a person has to pay attention to where its coming from. As others have said personal transitions/change can be intimidating. As far as the world in general...that's a big concept to think about. I also think many young people feel scared when they finish high school and then when they get to the end of University. Its great you think you can make a difference but be careful not to get too ahead of yourself - its hard to fit the earth into your backpack lol.