Your account value is based on how much Steem, Steem Dollars and Steem Power you own and simply converted in US$ at the current rate. When the price of STEEM falls, your account value falls too, when the price of STEEM goes up, your account value goes up too. So, basically, you're not loosing steem, simply steem is losing value against the US$.
@fede93g is right
thank you
@artemk yes i did to few of them but still my voting power is above 80%. shouldn't we upvote other's post to save our wallet?