I'm not sure "sadness" is the way I'd describe it, but returning back to the real world is a bit weird if you've been in for a few hours. I've always attributed it to the wind-down. The crazy part of onward is it literally invokes a prolonged adrenaline reaction. At least it used to, it's not nearly as much anymore. Leaving can be exhausting. It's definitely part of the addicting aspects. The first few times when I dove to the ground because I heard gunshots near me was exhilarating. I find myself wanting increasingly more intense moments.