Something a bit strange I noticed while marching

‌Reading through posts here... I don't remember every single detail, but
At first, we packed our gear strictly by the book when we started, but right before departure, we'd take things out here and there to significantly reduce the weight.
By the time we became Sergeants, some guys were even putting boxes in their packs just to maintain the shape.
At first, my shoulders and ankles hurt and everything was aching, but after walking for a long time, there comes a point where the pain just stops—I'm not sure if it's because of numbness or if I just got used to it.
From that point on, I felt this surge of euphoria. I don't know what it was, maybe something like a runner's high.
Actually, I felt like I wanted to walk even more and was disappointed when the march ended.
As long as I didn't get blisters, I think it was a pleasant experience.
I wonder if people these days walk while looking at their phones during marches too.