I remember doing this as a kid (though not from a chair!). Or at least trying to do it. For i don’t think i could ever completely commit myself to it and instead sort of stumbled backward. Which reminds me of a football game where a team ran a trick play in which part of the trick was to have a receiver suddenly keel over so as to distract the defenders opposite him long enough for the play to work. So the receiver took a couple steps, stopped, and suddenly fell backwards stiff as a board without so much as flinching a muscle. Now that really impressed me, for even with helmet and padding i couldn’t imagine myself doing that in a million years. But unfortunately it didn’t work. For the defenders were like “if he dies, he dies” and went about their business as usual.