I've had it hit me hard, and other times not so bad. I live at 700-800ft - when I was younger, stupider and in better shape, we would pull into the trail head, throw on our packs and start blazing up to 9500 - 10,000ft.
That's when it would hit me hard, didn't matter what shape I was in. Now we are a bit smarter and walk in at about 8000' set up camp and start going higher the next morning. It's still a killer for the first few days, but at least not getting so sick. Usually, I'm telling myself " hey, I'm getting used to this, this isn't too bad now" about a day or two before we are scheduled to head home - never fails.
That's when it would hit me hard, didn't matter what shape I was in. Now we are a bit smarter and walk in at about 8000' set up camp and start going higher the next morning. It's still a killer for the first few days, but at least not getting so sick. Usually, I'm telling myself " hey, I'm getting used to this, this isn't too bad now" about a day or two before we are scheduled to head home - never fails.