There are several possible reasons for the dock disappearing on your Mac, including system errors, dock concealing settings, and software bugs. To fix the issue, you can try restarting your Mac, restarting the dock, adjusting system preferences for the dock, pressing option keys to unhide the dock, and resetting fullscreen mode. Upgrading to the latest version of macOS may also resolve the issue. It's important to note that you should be cautious about data security during the troubleshooting process and consider using data recovery software if necessary.