It is possible.
If you leave an order overnight and the opens way past your SL - you can get a loss that is way higher than the SL level you’ve set.
Also, if you have hedged possitions and one gets closed out due to a margin call and the other is no longer hedged this can turn your account to become negative.
For cases like this it’s good to work with a regulated broker or at least one that has negative balance protection.
Ever since the new ESMA regulations came into effect all EU regulated brokers must provide said protection to their retail clients. So, yeah. At least that is a possitive of the ESMA regulations…