I'm fairly new to (Math) Stack Exchange, so I am hoping the community could shed some light on this: I answered a user's question, in a comprehensive manner, and the user up-voted and accepted my answer, even commenting "Thank you so much", so I received reputation for both of these actions. After a day or two, I check, and my answer has been "unaccepted", and thus revoking some of the reputation I received. I could understand if someone posted a different, more detailed answer, but no other answers have even been submitted. The question the user posted hasn't changed either. So I can't see why my answer was unaccepted. Is it possible for other users to unaccept my answer? Shouldn't some reasoning be provided when a user unaccepts an answer in this situation?
It might be that upon further reflection they realised that the answer is not as clear to them. That happens on occasion, and it happened to me several times in the past (which is quite annoying, to be honest, especially when the answer is accepted very quickly).
There's no need to alarm, and you could leave a friendly comment under the question (or under your answer, if the OP had commented there) asking if something is unclear.
If, however, this is somehow a pattern, that a certain user unaccepts a lot of your answers, do let us know by flagging one of the answers with the free-form flag.