The man was a neg most likely. It's purpose was to scare you and feed off the energies you threw out when terrified. Either that or it was the dweller on the threshold (which is basically your fears personified in the astral). Both are basically thought forms I believe.
As for what you can do, I'll let someone with some more experience with this kinda stuff handle it.
As for what you can do, I'll let someone with some more experience with this kinda stuff handle it.