http://revach.net/article.php?id=4161

Section: Tefila   Category: Tefila
The Arizal To Rav Chaim Vital - Stop Looking At Me
Rav Shmuel Hominer in Olas HaTamid brings the following story about the Arizal's kavanos HaTefila.  One Shabbos Rav Chaim Vital had a terrible pain in his eyes.  He went to ask his Rebbi the Arizal why this was happening.

The Arizal told him that one of the reasons is because Rav Chaim davened in the same Shul as the Arizal and always sat on to the Arizal's right side.  He would stare at the Arizal to learn all his hanhagos in great detail.  The Arizal would have Holy kavanos during his tefila which brought down on him a great light from above, which Rav Chaim Vital should not have looked at.

The Arizal told Rav Chaim Vital that he should not look at him during Shema, when he bows by Modim, and when he answers Kadosh, Kadosh, Kadosh by Kedusha.  These were the three most awesome kavanos.  Rav Chaim Vital followed his Rebbi's instructions and his eyes became better.