If you plan to sell do it when everything looks fine, often drops are only temporarry. Selling or buying during falling price is gambling and doing the exact opposite of what you think is good idea might be a good strategy when the price is falling, it would have been for me at least.
It was previously overpriced a lot, fueled by DNM implementing monero, now it turnes out no one i able to withdraw xmr from oasis and alphabay, they might take the money and run or just drop support for it.