From what I can gather and explain, here is what most likely happened that made bitcoin pretty much crash to $3350 or so back in Mid March. The coronavirus was finally taking a toll on the markets, and BTC seems to be correlating with stock indicies. That week there was a huge dump in many global markets and bitcoin followed. Then bitcoin kept going lower and lower most likely because BTC was at a profit for most investors but their stock positions were at a loss, hence they sold to make up for it. It led to more selling and eventually the long liquidations started.

Bitmex is the largest exchange and provides most of the liquidity for many of the traders. However BTC in Feb was over $10K and many were assuming it would hit a new ATH since the halving was approaching, hence they opened leverage positions and when it broke the $7500 area there was nothing but long liqudations after long liquidations and pretty much there was a $1 billion of long liquidations and no bidders, hence the exchange went down and as a result it saved BTC from going to $0.