I have lose 4 BTC in Tow months Please any one tell me reason for Crypto currency breakdown

I have lose 4 BTC in Tow months Please any one tell me reason for Crypto currency breakdown

Hello guys greeting all of you,i invested 4 bitcoin through poloniex before three Months but unfortunately my balance is only 0.10657657 BTC . i am so worried about it can any boy explain what is reason behind this .i am using poloniex for trading , should i use an other platform to earn or there is some other reason ? please tell me friends ,give me a batter suggestions,

Almost all coins price is going too down ,i don,t know how can i get back my BTC