I didn't sleep well, and then my eyelids swelled up and folded together to form a multi-layer eyelid.

It is recommended not to drink water for two hours before going to bed. Drinking water makes your eyes more swollen. The other thing is not to stay up late and keep a good sleep.

Also, you can use a metal spoon, put it in the ice, and then stick it on your eyelids to relax.

You can try this method, because I can change my double eyelids back to single eyelids. You should be able to turn multiple layers into two layers in this way.