Bitcoin should be invest in top class coin which is running in the crypto market with strong market cap. I think you invested your bitcoin in very cheaper price coins which has no any existence in the market and cheaper coins are mostly used for pump and dump policy. some new people entered in the market and due to lack of knowledge of trading, people mostly stuck in the dead coin which have a huge quantity supply and not any demand of particular coins.
you can cover your 20% bitcoin by selling all altcoins and buy some solid coins for long time and you will recover all loss of bitcoin.