During my captivity, a rare poison, Skilna Bragh, was given to me…— Arya to Eragon
Skilna Bragh was a drug used by the Broddring Empire which removed the ability to use magic. If consumed, it poisoned the recipient, usually killing them painfully in merely a few hours. However, elves such as Arya could resist its effects for longer by inducing a healing coma-like state. This enabled Arya to remain alive for long enough for her to reach Tronjheim and the one antidote, Tunivor's Nectar.