If you're feeling sleepy and want to wake yourself up — and have 20 minutes or so to spare before you need to be fully alert — there's something you should try. It's more effective than drinking a cup of coffee or taking a quick nap.

It's drinking a cup of coffee and then taking a quick nap. This is called a coffee nap.

It might sound crazy: conventional wisdom is that caffeine interferes with sleep. But if you caffeinate immediately before napping and sleep for 20 minutes or less, you can exploit a quirk in the way both sleep and caffeine affect your brain to maximize alertness. Here's the science behind the idea.