This is a pretty simple question, but initial research only seems to provide the opposite end of the spectrum. What I'm wondering is if there are any known side effects of living in an environment with an increased amount of air pressure.
Say, for instance, humans colonized an Earthlike planet which had twice the air pressure at sea level than we have here (disregard whether or not this is possible, that may be a subject for a separate question), or say humans wanted to build an underwater facility and decided to save money by equalizing indoor with outdoor pressures.
I know there are limits to how much you can compress a gas, but I assume humans wouldn't feel too good as they approached those limits. My question is what pressures would cause problems for humans, and what would those pressures/problems be?
Assume any pressure would be achieved gradually, so no worries about explosive compression or anything like that.