@simrin-- Some people are more sensitive to caffeine than others and experience jitters and anxiety from just a cup of coffee. Other people can handle more. Unless you also develop other poisoning symptoms like vomiting and heart pain, I doubt that only a cup of coffee will cause caffeine poisoning.
I think the main risk of poisoning comes from caffeine supplements because the dose may not be well regulated and people may take too much. In fact, there was a man who died from caffeine poisoning a few years ago because he took too many caffeine supplements. It was in the news.