everyone has their own analysis, if they analyze that bitcoin will go down again, then I think selling it now is the best thing, and can later buy it back at a cheaper price so that it gets more bitcoin, but if the analysis is wrong, then things it is a risk
That is called speculation whenever you want to buy the Bitcoins or sell Bitcoins please see theprice chart for previous one month and one week off chart.
If this both chart is dump you can invest on bitcoin at the same moment and sell it when the value goes big every time.