I lost more than half a bitcoin in just a single mistake in less than a few minutes on day a few weeks back.
I used to do margin trading on bitmex and it was just a usual day for me but on that day I was outside my house and didn't had access to internet and I had a few of my longs in place right before leaving the house. But when I got back in the evening I was shocked to see the price below my liquidation price and all my bitcoins earned from the past month were gone.