Thirst faint (underwatering)

What's happening

Fittonia has thin, soft leaves and shallow roots, so it loses water the moment the soil dries out. With nothing left to draw on, the whole plant droops and collapses in a matter of hours. It's the plant's famous fainting trick, not damage — the leaves are still alive and waiting for water.

How to fix it

Water it right away. Pour slowly until water drains from the bottom, and if the soil is so dry it repels water, bottom-water: set the pot in a few inches of water for 20–30 minutes, then drain fully. The plant usually perks back up within an hour or two. Going forward, keep the soil lightly and evenly moist — never soggy, but never bone dry — and check it every couple of days, since nerve plants dry out faster than most houseplants.

This is general guidance based on common symptoms; individual plants vary.