I'm not an expert and you should probably listen to the other comments but for me it turned out to be stress. I have been using a Garmin tracker extensively and when I go on a longer vacation and stop thinking about work my stress drops tremendously and correspondingly my deep sleep goes up. The Garmin is not super accurate, but I find it does a good job pointing out trends. Something to consider and it's a lot harder fix than just reducing caffeine consumption or stopping alcohol consumption.