So there you are. Relaxing on the couch with the kids after a long day. Watching a bit of telly. And the next thing you know, your toddler decides to turn ninja and propels himself off the couch at warp speed. Enter the 'Dad reflex'. What a pro.
To summarise, there is no such thing as 'relaxation.' More a heightened state of 'PERMA-ALERT'.