IMac not waking from Sleep after Sierra install

Hi all,

My iMac won't wake from sleep after upgrading to Sierra a couple days ago. I need to force restart the machine. The system still looks responsive - keyboard still responds when I hit capslock etc - but screen remains blank.

According to quick google search this was an issue during the beta with any kind of display related drivers. Can anyone confirm? I use Nvidia webdrivers but don't want to uninstall them unless I have to.

Thanks.