Breaking formation and legging it was a really bad idea right up until the introduction of breech loading infantry arms. Cavalry is pretty much useless against tight infantry formations, but it is really hard for an individual on foot to deal with an opponent on a horse. If that individual has dumped his weapons, and probably any armour if they had any, and has his back to the horseman it's just target practice.

Pretty much any wound from a well swung cavalry sword is going to be disabling although not necessarily immediately fatal, and being run down by upwards of half a ton of horse with flailing hooves isn't going to do you much good either. Once you're down then there's a bunch of infantry coming up on you, and their main interest is seeing if you have got any food or valuables on you, and making sure you don't come back next year. No MASH units until Napoleon, if you were on foot you're not worth keeping alive for ransom, and why waste food?