I've noticed since I quit drinking that I generally feel more awake and energetic, but after a few hours of focusing, I grow tired.
I've ended up taking naps most days.
For years I've had a job that puts me on the road a lot and when I drive long hours, I am very aware if I'm getting sleepy. In all the years I've been doing that, there's were only a couple of times I ever pulled over and fell asleep on the side of the road. But when I was on the road the first few weeks after quitting, there were several days I pulled over and just crashed right out.