OH MY GOSH. I had the exact same experience as the two of you. Seventh grade. A teacher made me watch it, and I had horrible nightmares afterward.
My teacher, Mr. Brogdon, was this great old retired Army officer. I grew up near Ft. Benning, in Columbus, GA. Mr. Brogdon was kind enough to point out that we'd be lucky enough to be killed in the first strike because Ft. Benning was the fourth highest value target in the U.S., and had enough firepower pointed at it to destroy it 250 times over. He consoled us with the following, "Most likely the Pentagon won't have time to warn us it's coming, because by the time they know the missiles are inbound they only have 13 minutes, and it's unlikely they'd confirm the missiles were real in time to get the word out. You'll just see a flash of light and then there will be nothing left of you except maybe a shadow where your body was..."
I had horrible, horrible nightmares for months. I'd be dreaming, and I'd suddenly see a flash of light and wake up hyperventilating. Or, I'd dream I was going off to camp or the river or whatever, and then Columbus was vaporized. I refused to go on the church youth group beach trip that year.
The worst came that summer, when I was home alone with my younger brother. It was a beautiful sunny day, and all the sudden the civil defense siren went off for no reason. I freaked. I knew that clearly this was the nuclear war. Unwilling to accept my vaporized fate, I dragged the sofa against the wall, flipped it over, and forced my brother into the cave. I grabbed pillows to stuff in the gap at the side, and waited for the end -- completely freaking the 10 year old brother out in the process.
My mother was sure I'd imagined the siren, and was trying to find a good psychologist until the news that night mentioned a small problem with the sirens that left many old people crouching under their stairs and in interior rooms.
Nice to know it wasn't just me.