Well, the fgs know I'm the ghost... they have no reason to kill me. I still vote, and I can still help outnumber them in the end.
If I am a fake god, it does not make me immortal. If we're using the version where the ghost can't do anything but vote, I'm at a disadvantage; if I vote with the mafia, others would flock away from that person. So I would vote for the mafia - but then I'm voting against my own team. I would probably just not vote, it might be too risky. If we play the version where I can still do anything, again, I'm at a disadvantage. I obviously can't do the classic fg tactic of blending in with the crowd. I really can't say anything, anything I say will have no meaning.
If I am a villager, then again... we only lose one vote (the fgkill) rather than two if we kill a villager. Sure, we might kill a fg, but probably not. The first vote is usually random - this way, we can avoid that and go straight to voting with reason. We also don't risk killing the seer/doctor. By round 2, we should have enough info to figure out a fg or two.
It's now or never (or possibly much later by chance). After today, if I'm alive, a tradesman is likely to trade with me. Ghost is a desirable role, it lets you participate even after death.