If you strap on a heart rate monitor and do an apnea ‘dry walk’, you will see your heart rate rapidly drop, even though you’re physically active. I have advanced students perform this to see how pronounced their dive reflex is. They sit on a chair breathing gently, then take a last full breath in, hold their breath seated for 30 seconds, and then stand up and walk (still breath holding). Responses vary by individual, but all experience a drop in heart rate whilst walking, some to less than half their resting heart rate.
https://www.deeperblue.com/the-mammalian-dive-reflex/