Many people have a similar problem, and in most cases it is because they lose their focus thinking about the win or thinking about how they look if they lose, instead of thinking about how to win and staying focused on the table. When your shooting think of nothing else, except how you plan to close out the rack, if you are down on a shot and others things begin cloud your thought's stop and stand-up clear your mind think of your plan and execute.
In most cases the mistakes made are things that are corrected very simply. When we are not focused on the table we begin to miss shots that we would normally make with 90% accuracy or better. It seems that for some reason things are just not working and we can't put our finger on the problem. One of the first mistakes that occurs when your mind is clouded with other thought's is taking our eye's off the object ball. Most players know that a major part of making a shot is staying down on the shot, following through on the shot, and keeping your eye on the object ball until contact with cue ball.
Like I said in a previous post to one of threads keep your mind clear, and play you game on the table, and treat each shot the same no matter how hard or how easy.