Hello I dont understand I bought for 4000 Eur one hour ago of Ethereum when it was going up, it stayed around the 10-20%, it started to decrease 5 minutes ago so I sold it and now cex.io just gave me 3500eur for it... wtf...

The %came from me watching livecoinwatch.. Cex.io doesnt have the accurate price ??
You can see that the market in recent days is fluctuating continuously and complicated, can see that bitcoin prices in recent days are constantly adjusted and still not a clear trend. So you trade at this point the risk will be very high because the price of bitcoin and altcoin will fall extremely strong. It can be seen that the price of ETH is decreasing sharply in the past few days as the market is falling, secondly the ETH is experiencing very big problems from the manufacturer which leads to the price of ETH is falling sharply.