^^^yes that is the endorphins at work. think about it this way.. our ancestors used to hunt for food which required A LOT of exercise everyday so it makes sense those who do not exercise everyday would have lots of health problems both physical and mental. our ancestors for millions of years used to chase down prey and outrun them, yes we have sweat glands and our prey did not.. so eventually we would catch them.
in todays world most jobs require a lot of sitting on the buttox so people are not getting enough exercise. thats why i exercise EVERYDAY. whether it be sex, weights, cardio, hiking, swimming whatever. people who say to only workout 3X per week are usually guys who work hard labor jobs, in that case they can afford to only workout 3X per week, but in my case i have to everyday since i spent 23 hours of my day on my ass in front of a computer or in bed.