Last week I barely did anything but guard idly on a half-court for around five minutes, I sat out on rotation, and could barely stand, was short on breath; felt like I was going to faint. Felt like shit the rest of the day.
I used to get this feeling as a kid somewhere in my upper stomach or lower chest, that felt like a thick iron rod pushing up against it or something, after I ran too much. I've been told it's normal, but for years I haven't been able to run for more than a minute or two without running into it.
Also, I've tried aerobic exercises in the past at the local Y and nothing has improved. I'm not fat or anything (at least I don't think I am), but I'm pathetically out of shape, and I'm convinced there's no way out.