For the last week or so I've had extreme shortness of breath, especially when I walk somewhere. My chest and back always feel heavy and tight and I get out of breath just moving around. Today I got really worried when I realized I wasn't able to talk and walk at the same time; I had to focus on getting air. Can shortness of breath this extreme still be anxiety? I thought it was a side effect from not taking my atenolol for a few days (pharmacy mixup) because that's when it started, but I've been back on it for four or five days with no improvement.