Is there a way to express "I'm lost" (in a metaphorical sense)


For example, you're talking to someone and he's trying to explain something to
you, and you have no idea what he's going on about. You could just say "I
don't understand", sure, but is there something more akin to the English "I'm
lost"?




How about...

> (話が)わからなくなりました。(←わかる(解る)+ない(無い)+なる(成る)+ました)(rather than just
> わかりません。/わからないです。/I don't understand.)  
> or  
>  (話に)ついていけていません。(←つく(付く)+て+いく(行く)+て+いる(居る)+ません)(rather than just ついていけません。/I
> can't follow.)

