It happens every day due to human emotion which is inbuilt. Panicking will cause you loss and regret. I had MTC 3000 coins and there was this news that the coins is being dumped and i panicked and sold off my 3000MTC only for the coin to move from $0.035 to $0.45 within the next 3 weeks after i sold off.
But I guess it's not too much regret. Many thus lost tens of thousands. The most important thing is not to panic. And treat tokens as if you don't have them. You have nothing to sell. But when the price will suit you, sell. Set a clear goal, not a "get rich".