That moment when you buy 1BTC at $2500, and then 3 days later someone buys it at $2000. But I'm guessing that it's the risk involved in investing, so what do I do now? Sell? Or hold on them?
If you held on to your bitcoins up to this point, you should be celebrating since you only purchased them at $2500. You actually made more than 100% of your investment. If you didnt hold, well, let it be a learning. 
long term is always a good option so you'll be able to feel the big blow out, bitcoin still in its early stage so a lots of possibilities to achieved bigger
value so just keep the fate.