It's extremely healthy and it feels good. It's psychologically healthy. It's the antidote to stress. People who relax like that have a less intense reaction to stressful situations, and they recover from them faster than people who don't. In other words, instead of a person's heartbeat going from 70 to 120 beats per minute during an argument and returning to 70 in an hour, it might go from 70 to only 100 beats per minute, and return to 70 in a half hour.
Stress is unpleasant.
Stress is dysphoria. When blood-lactate levels drop during relaxation, it stays down afterwards. This is one reason you feel so good afterwards. Blood-lactate has something to do with anxiety. When you measure the blood-lactate level of someone who feels anxious, you'll find a lot of it.