How often have we heard the advice to take a deep breath when we're stressed? It's ubiquitous, and the logic is almost there; We know that steady breathing can help activate your parasympathetic nervous system (the opposite of fight-or-flight), so taking one deep breath can get that started, right?
Not exactly. As Huberman explains, "If you are stressed, taking a deep breath is not the best solution. If you just take a deep breath, actually you will increase your heart rate through a process called respiratory sinus arrhythmia."
What he suggests instead, is taking a double inhale through the nose, and a long, extended exhale, also through the nose."[This] is by far the best way, and it's not a hack—this is what you do when you're in a claustrophobic environment, and you do it every 1-3 minutes during sleep," he notes.
Huberman explains that when you do this technique (which he calls a "physiological sigh"), you naturally activate the neural circuits in the brain and body that shift from sympathetic tone—alertness and stress—to parasympathetic. "And for most people," he adds, "it takes only one so-called physiological sigh [to] completely return to a calm state, and this is, as far as I know, the fastest way to shift yourself from stressed to calm."