Screen doesn't come alive after a call.

[Blapper]

For some reason the screen on my Experia Z5 Premium stopped waking up when I take it down from my ear. Obviously that's a pain because I can't work on the phone during a call or enter pins or 'touch 1 for customer service' etc. I've had a couple of updates since, but it is still the same. Anybody got any ideas please?

[Uliwooly]

Make sure that there's nothing covering the proximity sensor and also make sure that it's clean. 

Settings > about phone > diagnostics > test > test proximity sensor.