The bear can't actually hurt you. To explain why, let's work through the history of how illusions have worked in Ars Magica, and why this was selected as a game design thing, and then the in world excuse for that design decision, OK?
In an early edition of Ars, illusions could create the illusion of pain, and could create illusiary consequences like illusions of wounds. If you illusion-died, you fell unconscious. Now, in that edition, to create an illusion required Cr, Im, and a requisite for the thing, so, a bear, for example, required An. In practice this meant that itr was often easier to learn the arts required to make a thing than to make the illusion of that thing, and pure Im was useless, as even lights, for example, needed a requisite.
People thought this was counter-intuitive: surely an illusionary bear should be easier to make than a bear? The problem with the change that was made (dropping the requisite) was that it meant that an illusionist could, effectively, be better at the core Arts of specialist magus in many, even most, TeFo pairs. Let me give you an example: say Ball of Abysmal Flame is level X, and an illusionary Ball of Abysmal Flame is X-10. Now, you may say "Ah, but the illusion just knocks people out. It doesn't kill them!" to which the answer is "So what? If all of your enemies are asleep, then your grogs can just knife them in the throats. Defeat in combat is defeat in combat." So we had this odd situation where Jerbitons were effectively better at using fire in battle than Flambeau magi. In the bear example, it means that if you are a Bjornaer and can turn into a bear, there are a ton of Jerbitons who can just make mock-bears which are as effective as you in combat, in essence, because asleep enemies are dead enemies, really.
So, now, Im doesn't make illusions, it makes species, specifically so that it doesn't make these complex, reactive things like a mock-bear. The reactiveness is hard, and best handled by a human brain. The bear can't give the sensation of pain, to wreck the combat effectiveness of illusions. Instead you need to be clever. Lure people into pits. Trick them into attacking each other. THat sort of thing. It's to break this problem of "Illusions need to be easier than X, but need to not be basically as good at X in overcoming obstacles."
Now, our excuse in the game now is that although pain travels through the body, and may even be triggered by haptic species, theoretically, the things the species would need to strike are within the body, and so the level would be ridiculously high. That is, your pain sensors are under the surface of your skin, so to target them you need to do a Lungs of the Fish sort of spell that gets inside the body. And even if you do that, it arguably doesn't work. Clearly, no-one has got it to work yet.
So, that's why things work as they work: we've tried everything that's simpler, and they just wreck the game a bit.
The next step, I'd argue, might be making illusions a lesser form of creation, so to create an illusionary bear, you CrAn, at a level, say 10 below that of a bear. That's what I'd do. I've thought about it a bit for a faerie game.