I sort of want one. Matching pajamas, cap, slippers, and a little candle I can carry around.

I've never seen one of those hats used IRL, but I get it.

If my room gets really cold, I can burrow in blankets, but since I'm not one of those weirdos who can sleep with a covered nose/mouth, my head has to stay stuck out and will still be cold.

I usually find a clean sweatshirt to hide the top of my head under or, in desperate times, origami my blankets up from behind my shoulders to tuck it in.

I always assumed it was a pun for kids, cuz I've only seen them in cartoons. A "night cap" is usually an alcoholic drink taken to help you sleep, but in a kids cartoon it's a literal cap worn at night.

It's a nightcap

Women's night caps were usually a long piece of cloth wrapped around the head, or a triangular cloth tied under the chin.[1] Men's nightcaps were traditionally pointed hats with a long top, sometimes with a pom-pom on the end.[1] The long end could be used like a scarf to keep the back of the neck warm.[1]

From the Middle Ages to the 20th century, nightcaps were worn in Northern Europe, such as the British Isles and Scandinavia, especially during the cold winters before central heating became available.[1] People tended to think that cold air was harmful, so a nightcap protected them.[2]

Nightcaps are less commonly worn in modern times, but are often featured in animation and other media, as part of a character's nightwear. Nightcaps became associated with the fictional sleepers Ebenezer Scrooge and Wee Willie Winkie.[5] The hat has become typical nightwear for a sleeper especially in comical drawings or cartoons along with children's stories, plays, and films;