By default, any new brush you create is only stored in the Brushes panel and is not saved elsewhere. All unsaved brushes, presets, and actions are temporarily kept in a Preferences file. Your only chance of retrieving unsaved brushes from that file is if you have regular backups; otherwise, if you lose them, they cannot be retrieved and will be permanently lost.
So remember to always save presets, including brushes, as files on your drive and to back them up regularly, just in case. Saved brushes can be lost due to significant computer failures.
... View more