Why does the Dock disappear on my Mac? It pops back up when I put the cursor to the bottom of the screen but does not stay there permanently any longer.
You've probably enabled Dock hiding. You can toggle this by pressing ⌥⌘D.
Alternatively, you can toggle it through System Preferences or by right-clicking the spacer between the apps and the stacks then turning Hiding off:
For me, I don't remember turning Hiding On, but I must have done it inadvertently. When I tried toggling it off, it fixes this problem.