I was working out in the gym when I saw people staring at the TV's, and saw footage of a plane in the side of a big building. I didn't know what or why since I couldn't hear the audio, but went home and turned on the TV there and watched it all day, afraid and mourning. I live near one of the biggest airports in the US so once I learned it was an attack, not just some horrible mistake, I was very afraid; every time I heard a plane go by overhead -- the last airplanes already in the air being landed -- I cringed, especially after I heard of the Pennsylvania flight that crashed to the ground.
I didn't know anyone killed in it, but I did know someone, a friend I grew up with who I'd lost touch with, who worked in the building; she was on the subway on her way to work, running late, so wasn't there at the time.
