I think its not risky beside if you want to use them anytime you can just convert some into fiat. Bitcoin is a good currency to hold either for short term or long term period specially now that the value keep increasing. Converting all your money into bitcoin does not mean you cannot use them when you need it so I think there's no risk with that
What you are telling is wrong investing whole investment to Bitcoins is always risky as you can see the price went down from 7800+ to 6700+ so who ever invested in high level is now i loss and suddenly he is in need of fiat currency then will have to sell in loss. So it is not good to invest fully in bitcoins but invest only that much amount which dont affect your financial position if the bitcoin price goes down.