Could be a power surge or some short interruption if they work on the lines sometimes. As long as your monitor isn't ages old I would probably guess at something with the power. I sometimes get mails that won't go through so I just unplug the power lines and wait 30 seconds and rehoook and everything works fine. One tech told me sometimes there are just too many users at one time and they have power outages for a second or two.
I wouldn't be too concerned unless this is a frequent occurence.