Apple released both watchOS 5.1 and iOS 12.1 recently, though the former update was quickly retracted after many users complained that their devices were rendered useless right after installing the new update.
Apple’s watchOS 5.1 update includes bug fixes and also the new emojis that are available in iOS 12.1, in addition to updated watchfaces, Group FaceTime audio and enhancement to the fall detection feature that is only available in Apple Watch Series 4.
It seems that only the watches from Apple Watch Series 4 were affected and the only solution was to seek for AppleCare, meaning that there are no ways for users to reinstall or revert to the previous software versions themselves. Users who install the update that was estimated to be around 10 minutes ended up waiting for few hours for naught, though there are also users who successfully updated their Apple Watches.
To avoid further compromises, Apple decided to retract watchOS 5.1 and re-release it when the issue has been fixed and tested.