Frequent mistake...Shire type Horses never even existed in Medieval Times, and most horses, even those carrying mounted Knights, were not much more than about 13-14 hands, and Nimble, quick animals.
The stuff about Shire Horses, and Knights being lowered onto Horses using a Block and Tackle, is Victorian Story telling.
If you look at the Bayeaux Tapestry, you will see that the Mounted Knights feet almost touch the floor....this was also true of Full Plate Armoured Knights in later centuries...Yes, the Horse had work to do, but as a full charge would only really occur, once the enemy were within about 200 yds, it was much more usual, for a full Gallop to be attained, to punch through enemy infantry.
In Jousting, the Horse's tend to meet at a fast canter, due to the Tilt being quite short, and Balsa tipped lances are used... but, yes...still quite dangerous.
In Medieval Jousting, very dangerous indeed...but then, so was Medieval life!