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?
I would hold them. It depends though for what purpose you bought them, if you bought them for just trading after price would go to 3000 then just wait until it reaches 2600 and sell but if you bought them for a distant future, hold it as it maybe the best investment you have ever made.
If you can't wait just withdraw them to cash and build a mining PC, right now it costs in Europe one with 5 RX480/580 GPU-S at 2300 EURO in total. Start mining Etherum or Zcash and you will make with the actual price of bitcoin about 400 and maybe a bit more USD in bitcoin every month.
There are a lot of choices, it's up to you. Personally I am withdrawing bitcoin to create mining PC-s , I see more value in that than in any other job regarding bitcoin for the moment.