Cityaznguy saidOK I'm gonna risk sounding like a nerd. But here it goes.
Apparently weight of objects changes depending on the distance to the center of the earth (due to gravity differences), even though the MASS has stayed constant. So if you are lifting on the roof of a high-rise building, the weights are going to feel lighter compared to when you're lifting in a basement. It also changes based on the lattitude of the earth. If you're closer to the equator, the objects are lighter and if you're closer to the poles the objects are heavier. So under similar conditions (e.g., ground floor), bench pressing 200lb in Alaska would feel heavier than bench pressing the same 200lbs in Hawaii. I believe the difference is about 1.5% which should be noticeable.
Of course if you're talking about similar conditions (i.e., same cities, same altitude), then yeah it's in your head.
Ok, I have to respond to this. If you knew the equation of gravitational attraction, then you would know elevation and latitude will NOT affect in any *meaningful* way how "heavy" the weight is. It would be beyond negligible.
If we were on top of Mount Everest, 25 lbs would technically weight 24.96 lbs. That is a 0.16% difference. Really negligible. You cannot "feel" that kind of change even if you were on the farthest point from Earth's center
(which is not Everest but it is well known).
Read up on the Gravitational Constant of the Universe as well as orbit free-fall. If the weight was in orbit, the Earth would still be pulling on it with more than the majority of the force it felt on Earth's surface.
The more likely reason why it feels heavier is likely due to what both Photosrus above me and Paul below me said. Or if this is not a point mass such as a dumbell, but rather a machine/lever/cable, as track_boi pointed out, depending on the configuration of the machine you may have to do more or less work to move the same weight due to a change in the moment-arms and pull force over a distance assistance. All elementary static mechanics.