I thought that at first. I think that, for one thing, it would be the passive form (förloras) - but actually it seems like the word for not knowing where you are is vilsen (which is an adjective, so Är du vilsen?).
vilsen has a wider meaning, more like 'confused'. The word we would use is vilse (if we're speaking about someone who has lost their way).
Tack! Wiktionary says vilse is an adverb, so would it be something like Har du åkt vilse?
(This dip in wiktionary has also led me to a word for "mistake", villfarelse, which I think is Gonewrongening).
Yes, it's an adverb. You can say Har du gått vilse?, Har du åkt vilse?, Är du vilse? (the first would be the most common).
We do not accept normal sentence structure with the addition of a question mark for forming questions.