Are there any records for what the annual rate of return has been over the years for casino backers?

Ok - firstly, wish I had found this thread about 5 minutes earlier, as I just dropped half a bitcoin in before coming here and reading that people are having trouble withdrawing ...

But hey ho. So I've put it all into the house, which I've done in the past, often with much larger amounts (had 10 BTC on the house at one point a year or so ago).
Almost immediately - as in a matter of about 20 seconds - I'm down by 0.05 BTC (£42 at today's price!) - this is a huge swing, judging by how I remember it behaving in the past! Does this mean that someone just scored a MASSIVE win, right after I invested? Is this normal behaviour?

Seeing as my investment, by my rough mental arithmetic, seems to have lost 5% of its value in a little under 20 seconds, does this mean that theoretically it could be wiped out in a little over 6 minutes? Or are gains and losses of this magnitude exceptionally rare?