Morbus

Is it normal to feel like lower body workouts really kick my ass as opposed to upper body? I am an inexperienced lifter and the only rationale I can come up with is that I'm working much larger muscles in my lower body. I find myself sweating bullets and breathing heavily during my lower body stuff but barely breaking a sweat on upper body days. To be fair, I do feel like I push myself a little bit more on lower body days. Any explanation?

What exactly is 'deloading'?