Lost Class Mod Item

I was in game with another person just now, and we were trading items. I tossed my phasezerker on the ground for him and it fell right through the floor of Sanctuary 3. Is there anything I can do to get it back or am I just screwed?

Unfortunately not. Sanctuary is well-known for having leaky floors, especially in the main area at the aft end where you spawn in. Best option is to trade rather than drop; otherwise, try dropping on one of the tables.