As you've probably noticed, some things - notably poison, paralysis, and confusion - stack when they're cast on you. Some good spells stack also. I've been asked "What's the maximum duration of these effects?"
The answer is: 10,000 game turns. In town, approximately 100 turns go by per minute, and this number decreases a lot as you go deeper into the dungeon.
So... if you have the maximum amount of confusion cast on you in town, you'll have to sit and wait 100 minutes for it to wear off. There's no way anyone would have the patience to do that to you, though.
FAQ: Maximum spell effect duration
FAQ: Maximum spell effect duration
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