Briefly here, on today's NY Times article on touch , and that warm touches (and who knows, maybe the playful punch in the arm or slap to the back of the head) results in release of oxytocin and reduction of cortisol. Oxytocin is released within the brain and triggers feelings of relaxation, well-being and warmth towards others. For more info look that hormone up on Wikipedia. Cortisol is elevated in people who are under prolonged stress and is associated with a range of undesirable health effects like cancer, elevated blood pressure, cardiovascular disease and if I remember correctly possibly diabetes. Oxytocin is probably signalling "its OK. You are not alone" "The threat is gone", or "we will fight this battle together".
So, reach out and support your friends, colleagues, team-mates and loved ones. It is likely to do a statistically significant world of good