"My favorite technique is relatively simple,” Rabin says. “Just breathe the way you breathe when you're sleeping.” Think long, slow inhales and exhales: "[Breathe for] five seconds in, hold for a second, [then breathe for] five or six seconds out. Just keep doing that, and try to fill your lungs as deep as you can and empty them as much as you can on every exhale,” he explains.
This simple technique activates your parasympathetic nervous system, which takes you out of a "fight-or-flight" response and into a "rest-and-digest" mindset. "Your body starts to wind down, and you're starting to tell your body, 'Hey, you're safe. You're safe enough to pay attention to this breath. That means you're safe enough to fall asleep,'" says Rabin.
As a general rule, just make your exhales longer than your inhales—that’s what stimulates your parasympathetic nervous system. But if you need something a little more prescriptive, you can try a 4-7-8 breathing practice. It’s the same idea as Rabin’s trick, but it just requires a few more seconds in between steps: Inhale for four, hold for seven, and exhale for eight.