Hey man,
same thing happened to me a few hours ago on XA, if i understood you correctly. Screen flickers in roughly 1Hz, i get 1s of normal picture and for 1s every second horizontal line is black + vertical ghosting lines. I think the phone got moistured, somehow.
The problem is probably in oxidized screen contacts, open the phone up and clean it with rubbing alchohol and/or desilled water. Do not use too much pressure and do not use harder materials. Toothpickes and soft toothbrush will do just fine.
Best of luck if you decide to open the phone yourself, Z series is made real tight inside. I'll try my luck on the guarantee first, since the phone is 3 weeks old. (: