OH! That looks bad!
Have you tried switching to object mode and then back to sculpt mode?
I notice you Dyntopo turned off also.
Try SHIFT+CTRL+Z to un-undo.
or try File > Recover > Autosave, and look for the last autosaved file.
or File > Save As, change the file name so you can go back if needed, > Save and then File > Revert > Revert, in the pop up box.
