I'm so sorry that happened to you lady. Certainly it wasn't aimed at you personally; perhaps he was having a poor day? I don't know. Either way, I would try to keep walking your dog. There is no way this guy will know what time you walk your dog and therefore there is little evidence that he will even show up again. How terrible that he scared you!

To answer your question, yes I have had paranoia that has sprung from something real. When I believed I was either being possessed or being surrounded by evil spirits, for instance, I had just before read Biblical passages about people being possessed. I believe I unintentionally absorbed the information and eventually began to disassociate in public places. At that point I would retreat to some place by myself (public bathroom even) and start casting out these demons (also absorbed from Scripture) until I felt peace again. Then usually, when I rejoined my group of people, I would feel this panic that I interpreted as demon possession very soon after and would repeat the process.