I had that exact shit happen to me. Got to a underwater treasure filled with a dragon's horde. And long story short, we get attacked, go back to the surface, hurricane we havent saw before right on us, and the onky things we kept was that IF you managed a save you kept 1 fucking item. Nevermind me saying to the DM : I put as many rings and necklaces and bracers on me as I can.
If you are going to give your party the allures of a big treasure and they beat your protections, you fucking better not pussy out and let them keep it all.