I play the game in full screen window. You did mess with it with the patch!
After patch 1.1.2 when i opened the game, it lagged horribly ... even when just turning camera around with mouse the game responds like 0.5-1 seconds later. It's horribad! Have noticed this thing before patch also when clicking around on other windows (firefox, outlook, skype, whatever) and then coming back to ESO the game sometimes remained in "background" mode in this way... then clicking out again and back to ESO window fixed the problem! Now after the patch 1.1.2 it's like permanent this way ... as the game were not in foreground but working in background with reduced responsiveness...