The Bitcoin lost half its value in 2013 because of a panic sell-off.
Actually, it lost a lot more than that. The spike to around $250 earlier in 2013 ended with a very quick crash to around $50 (80% loss). The subsequent spike to around $1100 at the end of 2013 was followed by a long, drawn-out fall to around $150 (~85% loss) over the following year.