Undine

Undinė means "mermaid" in Lithuanian.

It is a very beautiful name... but it still makes me shiver, because of a horrible congenital disease called Ondine's curse (Ondine being a variant of Undine). People with Ondine's curse have an inborn failure of autonomic control of breathing, which means that they stop breathing when they fall asleep (so they always have to sleep connected to a ventilator), or, in the most severe cases, that they have to actively control their breathing all the time.