Sounds like you are convinced you should sell. I don't think anyone unprepared for down days should be in stocks like this. Before you invest, be careful to consider the downside risk, not just the potential upside. Volatile stocks go down AND up, all the time, and never just one way.
I think you have to have a pretty strong stomach to not let days like this bother you.
This is my opinion, as a current investor in ACTC, and is not advice. You should seek advice from a licensed financial advisor.