It is very easy to restart the Xperia Z. Just hold power and Volume Up buttons for about 15 seconds. Your device should vibrate 3 pulses in a row, It should now be off, and don’t plug it in anywhere. That’s all to it, very simple. If you want to avoid doing this everytime, just to restart. Then consider rooting and flashing a custom rom , as most custom roms have a restart option in the power button menu.