Invest and hold that's all I can say. BTC price is ridiculous right now. It's not as stable as last year's price. By the end of 2017 it pump really high that traders celebrated endlessly. BTC price might be the effect of the world's economy.
Im pretty sure of that, i still invest and hold because i do believe that this coin has its highly profitable investment opportunities many are still attracted on this coin eventhough many are suffer from dip stage. On the other hand, people behind the project are trying their best to satisfy the users and trying to restore the price of the coin in the market.
Nothing special to do if bitcoin decreases on the exchanges. Try to follow the trend by making price analysis on your own. Nothing else can be done to understand the main trend of bitcoin.