I'm surprised nobody's posted this possibility yet (that happened to me once):

I was scheduled for a week-long business trip, leaving early Sunday morning. On Friday before the trip, one of my cats became visibly ill. I got her into the vet hospital asap where they diagnosed her as having organ failure from previously undiagnosed diabetes. They tried to stabilize her before I left for my trip, but early Sunday morning, literally as I was about to walk out the door, "The Call" came. It was truly horrible but I couldn't at that point cancel my business trip. I'm sure I was visibly sad but tried to hold it together through security and whenever dealing with people, but when I was sitting by myself in the gate and on the plane, I let myself cry quietly. I've never been able to hold in that kind of grief, but I tried not to be a disturbance to anybody around me.

I wonder what the TSA SPOT people think of that kind of thing.