“A person is always responsible for his actions (i.e., damages caused), whether he’s awake or asleep.”
We learn in this Mishna that one needs to make a maximal effort not to cause damage with his body, not only when he is awake and is in control, but also when he is asleep and acting without any ill intent. From the straightforward reading of the Mishna, it seems that a person must pay for such damage under any circumstances.
Tosefot, however, citing the Jerusalem Talmud, states that a person is responsible for damage he causes to the property of another in his sleep only if the property was near him when he went to sleep. However, if another person placed property near the sleeper after he was already asleep, the sleeper who causes damage while asleep is not responsible. The reason, writes Tosefot, is that in the latter case, the one who put the property there is considered as having caused the damage.
Bava Kama 3b, 4a
