everyone for your scary experiences. Some sound very scary.
My dd was about 2.5 months old when I put her on a couch while I went through a washing basket to find clothes to wear. She was happily sitting up in the corner of the couch (corner unit) and I turned around for maybe 2 seconds to look at the washing basket and heard a squeak, then I turned back to see her sliding off the couch head first onto the floor. Poor baby screamed and screamed and I cried, but she was fine. She must have just thrown herself forward whilst sitting up. Now if she's on a couch/bed/chair/etc it's only in the arms of an adult. Very scary.