If the player changes dimensions - either via /execute in <dimension>, or upon exiting the End portal - with the Nausea effect active, the Nether Portal overlay will briefly appear and fade out a moment later. The nausea "wobble" will also disappear for a short time after the portal animation has concluded, though this may also just be a symptom of MC-196428.

This does not seem to occur when entering the End via portal, only when returning to the overworld from the End or when entering the End via command. As custom dimensions can, for the most part, only be accessed via command, this is guaranteed to happen when entering a custom dimension.

Steps to reproduce:

• /effect give @s minecraft:nausea 1000 0
• /execute in minecraft:the_end run tp @s ~ ~ ~
• Behold yonder purple swirl.