hello little ern,
hope you've recovered ok.
Regarding the original accident, there is atleast one alternative to the elastic (tension remaining in the drive belt) and the electrical (discharge of start capacitor, or turning of motor due to magnetic condition) which is this :
you are ripping a narrow piece (say one eigth inch thick )from the side of a board (or sheet) (wood or mdf). The piece which is removed (the thin piece) can end up in all sorts of awkward places, such as bottom front edge wedged against far end of the sawblade hole in the sawblade insert (stopping the forward progress of the workpiece) ; sometimes on shorter boards the cut off piece can instead catch its front edge up inside the front of the bladeguard (I had a piece up here a while ago I couldnt work out where the smell of burning wood was coming from !). Another place the offcut can end up is going through the blade hole in the table insert directly next to the sawblade. Depending on the off cut's length and thickness, it can fall through and into the base of the saw ( and up the extractor pipe), remain in the base, jam between the side of the blade and the side of the blade hole, OR jam between the blade and the saw casing / blade mounding mechanism. I dont know the design of the saw you had the misfortune to have the accident with, but I've known other saws where such an offcut has become wedged between the arbour mounting bracets and the blade, in a bent condition. If you disturb this (ie knock the blade or the offcut to remove it ) the energy stored in the bent offcut can be enough to spin the blade. Perhaps this was the cause of the blade spinning after isolation from the power supply ?? I hope I haven't bored you silly , I only mention it because I've seen sprung offcuts cause blade spin on my own machines, & this knowledge might help others avoid a potential accident. Furthermore, when you go to look and work out why the blade spun, unless you saw the offcut jammed in there first, you wouldnt know why the blade had moved.
I always ask myself now, "whats happened to the bit Ive cut off" because, if I cant see it its ususally got itself wedged somewhere it oughtn't to be eg up in the guard.
REgards, Catface.