In this website as far as I know we are allowed to down vote any answer or question by losing 1 rep. The problem with this system is that people with bad ethics can answer a question and down vote the other answers despite them being good or not. What I want to ask here is why is it even allowed to down vote answers in a question answered by you? It should be only allowed to vote in other answers, if you do not have any answer in that same post.
Similar situations and issues to the one you describe sometimes happen. It occurred to me that I downvoted a post and I left a comment. Moments later some of my posts were randomly downvoted (see e.g. Taking revenge on me because I publicly downvoted and commented). Nonetheless, I believe that downvotes (and upvotes) should have a mandatory associated comment that motivates the downvote, in a similar fashion to the peer-review process that research papers need to go through. This feature or similar ones have been requested by several members of the SE community. See e.g. these discussions https://meta.superuser.com/q/7223 or Encouraging people to explain downvotes.