Physical exercise - enough to get the endorphins going - is pretty good. A brisk walk, a run, chopping wood; all of them help. Sex is probably the best soporific - what was it Aristotle said about "post coitum...."?
Looking at a computer screen is the worst; your brain is racing, your body is doing nothing and your eyes are getting all scratchy.
So turn off your computer and turn on someone else!