I'm not an expert by any means, but I do like to watch stocks in situations like this. Usually you see the following:
1) Day 1: A big spike down and then fairly steady the rest of the day.
2) Day 2-4: A series of small movements (usually down) as some people take a few days to decide to sell off.
3) Day 4-7: People realize that they overreacted and bargain hunters swoop in. The stock gains back a significant portion of the losses it has taken (but not all).
So there are a few strategies to follow.
[*]Sell. If you want to sell, (A) Sell now (and maybe buy back in around day 4 if the price fell further from when you sold it) or (B) Sell around day 7 so that you get better prices than right now because you missed the big spike down.
[*]Buy. Buy around day 3-4 when prices are most likely to be near the bottom.
[*]Hold. Forget there was a spike down, you missed it anyways, so what can you do? One thing about this option, is that Pfizer is one of those stocks that can just sit there for years and not move (
in 5 years, it hasn't moved, and it seriously underperformed the market). If you hold, make certain you are in it for the very long haul with Pfizer. Don't think of Pfizer as a hold if you are planning on holding it for less than 10 years.
Me personally, I would sell and see if you can buy it back in later, taking a nice profit in this double transaction (use either method A or B above). If it doesn't work out and you don't buy back in, well, Pfizer wasn't a great stock to begin with so you don't really need it.