i had one (i think?) just now, that was pretty scary. i had a large bag of books (probably 45 or so pounds) that i was lifting up to work on. i dropped it while having it on my chest like a sash, and it fell down my back, pinning my neck to the back of the chair, strangling me. i couldn't lift it up because it was stuck on something, and i still can't tell what. i was stuck like that for about 30 seconds unable to breath, and i eventually got unstuck by pulling a small lever to lower my chair, making it drop 13 inches or so. it was really unpleasant and although i can probably hold my breath a lot longer than that, my vision started fading into blackness and it was a big relief to get unstuck. it would suck if my algebra books killed me.
anyway, share.