Maybe it's just me...but over 2 years of holding YMI, I've noticed that it continuously follows a "U" pattern throughout the day. It will be high early on, go low midday, and up for the end. Or the opposite, be low, go high, close low.
Then there's days like this, where there's a random unexplained series of 100,000 share buys in 2 minutes that brings it to a crazy high, then it just loses all that momentum and goes back to ground 1 in about 20 minutes as people sell off that spike.
What's even more aggravating is when you see it happen, but you can't convince yourself to sell and get back in immediately because you feel you may lose out on a potentially higher spike, or a trading freeze as they decide to execute a merger (happened to me before).