There's some way in which, in every town save the one in which you were born, you hold an extra inch of air in your lungs. Not so as you'd notice, day to day. You can run; you can sing and talk and dance. Your lungs meet your requirements. But you never get down to the bottom of your breath, and so that inch of air hunkers there, fallow, stalling, until such time as you can get around to coming home.
If this is all sounding a little bit "Waiting to Exhale," it's because I have been.