Why have I lost BTC or some of my investment - I have just logged in after awhile and it's gone?


We have no control over the market price going up or down. Please remember this is similar to shares, if the shares go down so does your investment. 

The coins you purchased will always remain the same e.g. if you bought 1.0 BTC at the price of $4000 and the next day the price has gone down to $3500 - you will still have 1.0 BTC.