If the value of that asset/position (of which trading symbol you're trading) decreases, the losses approach the value of your margin. Keep in mind that should you have positions in several symbols of the same trading pool, a total margin requirement would be calculated for all of your positions.
Please note accordingly, forced liquidations are executed on the account level too. In the case of forced liquidation, you would lose all of your margin balance, i.e. your margin balance would become 0.