Monsters & Treasure is a little vague about the details of ghoul paralysis: no mention of how long it lasts, or whether it's a paralytic poison that can stop a person's breathing, a chilling touch that causes general immobility, or an overwhelming fear that prevents most voluntary actions, but not speech. As a consequence, later editions famously interpret ghoul paralysis inconsistently; sometimes, elves are immune; sometimes, it's permanent unless cured; sometimes, a duration roll is added.
In Chainmail, wraiths, wights, ghouls, and apparently even zombies have the same paralyzing effect, which appears to be fear-based rather than poison-based. The effect isn't permanent and can be easily ended. I think from now on, I'll use the following interpretation:
In the presence of ghouls and other walking or ghostly undead, all morale failures result in a paralyzing numbness instead of retreat or panicked flight; the direct touch of such a creature will also automatically cause this fear paralysis, preventing those afflicted from attacking, defending, or assisting others or themselves in any way and rooting them to the spot until all undead in the area are slain or driven away, or for a full turn at the least. Victims do get one attack on the round they are affected, but are vulnerable for the rest of the combat unless aided.
Elves and any character with 4 or more hit dice are immune to this effect and can shake victims out of it, if they can touch those afflicted; Remove Fear will also work. If ghouls are still present, victims can be paralyzed again.