VM machine automatically rebooted

Can someone explain why one of my Ubuntu server was rebooted in the middle of the day?

Time is in PDT. That's a production server and therefore my website went down. I need an explanation on why there were no warnings. Plus, looking at the Azure Health Dashboard everything looked ok in the West US datacenter.

I also find absolutely outregeous that I have to post on a public forum for issues lke these.

Please provide an explanation ASAP.