Seafloor

You yell for help, but no answer comes. You suddenly realize... You don't remember anything about what happened before you were stranded underwater... And why did you have a knife... And how didn't you drown?? You suddenly see a boat approach, you wave your arms, and splash frantically to get it's attention. It sees you and turns to pick you up. You board the ship... and the boat is empty. Not one soul is on that boat...

What do you do?