Yes, antibiotics can cause this. It's not necessarily an allergic reaction, which would more likely manifest as skin problems or breathing difficulties, not anxiety. It's because antibiotics kill things in the body besides what they're targeting, and these things are part of normal mental health. Some of this you've heard of, which is your probiotics. Antibiotics are indiscriminate killers. Knowing this should ease your mind, and if you do ease your mind, this probably goes away. If it lingers, it means the experience so frightened you the brain internalized the feelings, and so if it lasts, therapy might be a good thing to do to learn some relaxation techniques, maybe learn some meditation or hypnosis, and get rid of it so it doesn't become chronic. But I'm guessing just knowing this is one of the reasons medical experts are trying, so far futilely, to stop giving out antibiotics so freely will allow you to relax back down. If you look at the archives on this forum, there are several threads with people getting this reaction -- it's not what happens to most people, but it happens to a lot of people. Peace.